Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MANUFACTURING EXPLOSIVES
Field of the Invention
The invention relates to a method of manufacturing explosives.
Background of the Invention
In the context of the present invention, the term "explosives" refers to
potentially
explosive and/or explosive substances and material mixtures serving as
blasting agents,
propellants, igniting agents or pyrotechnic charges or used in their
manufacture.
Numerous applications require explosives, and in particular propellant charge
powder;
examples of such applications include blasting technology and the propelling
of
projectiles. It is thereby usually necessary for the explosive to be in a
specific, variably-
sized cube-like or compact form, for example as a powder or a granulate,
whereby the
explosiveness of the e.g. nitrocellulose and/or nitroglycerin-based raw
explosive does,
however, pose special problems as far as its processing.
Thus, in the manufacturing of propellant charge powder, a differentiation is
essentially
made between processes which use solvents and those which do not.
In the manufacturing of solvent-free propellant charge powder (POL powder),
one
conven-tional processing method starts with a humidified
nitrocellulose/nitroglycerin
mixture which is dehydrated and gelatinized on heated rolling mills. This is a
manual or
semi-automated process using very complex equipment, whereby a sheet is
produced at
the end of the rolling process which is then spooled and extruded to its
desired geometry
in a hydraulic press.
In contrast to the above, US 4,963,296, or its corresponding EP 0 288 505 B1
or DE 36
35 296 Al, discloses a method of manufacturing propellant charge powder in a
solvent-
free process in which a shearing roller processes the humidified raw powder
mixture at
an elevated temperature. The raw powder mixture is thereby supplied
continuously,
continuously removed at the end of the shearing roller as a gelatinized mass,
and
immediately thereafter continuously granulated. The resulting granulate is
then
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continuously fed to an extruder, by means of which it is molded into strands
of powder
which are processed into the finished powder by cutting or other finishing
process.
With respect to the dehydrating and gelatinizing, this method represents a
considerable
improvement over the initially mentioned POL process, whereby processing the
granulates in an extruder has to date not yet been able to be reliably ensured
since high
melt pressures develop in the press when the granulate is being compacted,
which is
coupled with considerable safety-related concerns and problems. In order to
counteract
this, the granulate was therefore mixed with original humidified raw material
and only
afterwards rolled out into a sheet at a roller and processed. The spooling and
the
compressing into a desired geometry ensues pursuant the above-described
conventional
method.
Aside from the complicated operation, the latter method also poses
considerable
problems. The produced coil exhibits inhomogeneities due to fluctuating or
poor
gelatinized quality of the raw, previously dehydrated and gelatinized or damp
materials
mixed together. This has a noticeable negative effect on the overall quality
such that
most propellant charge powders are still being manufactured by the initially-
cited
conventional roller method.
A further improvement was achieved by the method described in WO 03/035580.
According to this method, immediately after granulation in a shearing unit and
subsequent processing into a granulate, the explosive material is formed into
a block by
means of an isostatic press. Because the granulate is fed to the isostatic
press while still
in a warm and plastic state, this prevents cooled or hardened granulates from
bumping
into one another in the press and from safety-related high pressure areas
developing at
the contact surfaces or the walls of the press during the compressing.
Yet even the cited methods still have difficulties in processing many various
raw
explosive materials. These difficulties can in part be attributed to the
initial adhesion of
the raw material to the shearing roller being too low to achieve a continuous
and
complete plasticizing of the explosive when processing the raw explosive
material in a
shearing unit. This insufficient initial adhesion prevents many compounds from
being
processed on a continuous shearing roller. Processing on conventional rollers
often also
causes great difficulties when processing in batches. In order to achieve
sufficient
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gelatinization, long processing times and/or complex shearing equipment is
often
necessary, which is highly disadvantageous both in terms of the process costs
as well as
the safety of realizing the process.
Description of the Figures
Figure 1 is a diagram which shows the process of gelatinized explosives;
Figure 2 shows raw explosive material prior to the isostatic pressure
treatment; and
Figure 3 shows the raw explosive material after isostatic pressing.
Description
The present invention is thus based on providing a method of manufacturing
explosives
which can be realized faster and more economically than the methods known in
the prior
art and which also exhibits a broader applicability respective the explosive
compounds
utilized.
This task is solved by a method in accordance with claim 1.
An important point of the invention is having the raw explosive first be
subjected to
isostatic pressing prior to gelatinization.
It has been shown that isostatic presses affect gelation properties,
particularly of nitro-
celluloses. It is thereby apparent that thermo-induced gels clearly differ
from pressure-
induced gels in their physical and structural properties. In particular,
pressure-induced
gels exhibit a lower modulus of elasticity, which facilitates later extrusion.
Isostatic
pressing of raw explosive thus yields a certain gelatinizing of the raw
explosive, which
clearly improves the processability of the raw explosive processed in this
way.
SEM images of raw explosive material containing nitrocellulose confirm that
there is a
great increase in volume of the nitrocellulose fibers subsequent the isostatic
pressing
step. This swelling suggests that the gelling agent is already dispersed
between the
polymer chains. The gelling agent partially dissolves the chain association.
The apparent
cross-linking is loosened. A further loosening then occurs during the
subsequent
processing, which typically takes place with shearing action.
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In a preferred embodiment, the isostatic pressing occurs at a pressure of from
1 to
10000 bar, in particular from 1000 to 7500 bar.
It is also preferred to effect the isostatic pressing at a higher temperature
than the
ambient temperature. Apart from the pressure-induced gelation, doing so also
effects a
thermo-induced gelation, which improves the pre-plasticizing of the raw
explosive. The
isostatic pressing preferably occurs at a temperature between 30 to 100 C, in
particular
between 50 to 90 C.
In order to obtain particularly good results, the raw explosive material
should undergo
isostatic pressing for a certain dwell time. Dwell times of from 1 to 20
minutes,
particularly 5 to 10 minutes, have proven especially advantageous.
In one preferred embodiment, the post-isostatic press gelatinizing of the raw
explosive
occurs in a gelation device comprising a shearing roller at a temperature
ranging from
30 C to 130 C, preferably at a temperature in the range of 50 C to 110 C, and
particularly preferred in the range of 70 C to 95 C.
To be understood as a shearing roller in the sense of the invention is a
roller as is
described in detail in DE 3536295 Al.
The swelling effected by the isostatic pressing of the raw explosive clearly
improves the
initial adhesion of the raw explosive to the shearing roller when being
processed on such
a shearing roller, which clearly improves gelation on the shearing roller.
In order to improve the processability of the pretreated raw explosive in the
gelation
device, the gelation device of a preferred embodiment comprises a rotating
drum with
internal lifting fittings on the inside of the drum and internal reverse-
conveying fittings
at the exit of the drum. The internal lifting fittings inside the drum cause
raw explosive
material which does not immediately adhere, falling away, to be automatically
re-applied.
The reverse-conveying internal fittings at the exit of the drum prevent the
material from
exiting.
In an alternative embodiment, the gelation of the raw explosive by means of a
gelation
device comprising a roller occurs at a temperature ranging from 30 C to 130 C,
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preferably at a temperature in the range of 50 C to 110 C, and particularly
preferred in
the range of 70 C to 95 C.
The warm explosive body yielded by the isostatic pressing exhibits an
elasticity which is
highly advantageous for its further processing. It is thus preferred for the
explosive body
produced by the isostatic pressing to immediately undergo the subsequent
gelling
process without any interim cooling.
The further processing of the gelatinized explosive can be effected as
described for
example in WO 03/035580. A typical procedure through to the final product is
depicted
in the process diagram attached as Fig. 1.
A preferred embodiment of the explosive particularly provides for immediate
granulating
after exiting the gelation device and the granulate being immediately formed
into a block
after granulating by means of an isostatic press. It is hereby preferred for
the granulate
to be fed to the isostatic press in a warm, in particular plastic state. The
ensuing block
can then be processed further in conventional manner, in particular by means
of a
hydraulic press.
In one preferred embodiment, the raw explosive comprises at least one
gelatinizable
component and at least one gelating component.
The gelatinizable component of the raw explosive preferably contains
nitrocellulose. The
raw explosive can however also contain gelatinizable components which in
themselves
are not explosive. Cellulose acetate is one such example of a gelatinizable
component.
The gelating component of the raw explosive preferably contains nitroglycerin
and/or
ethylene glycol dinitrate and/or nitramine. The raw explosive can however also
contain
gelating components which in themselves are not explosive. Examples of such
gelating
components are typical plasticizers such as e.g. phthalates.
The raw explosive can also contain explosives which are neither gelatinizable
nor
gelating. Examples of such explosives are RDX, HMX, PETN and nitroguanidine.
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A particularly advantageous explosive to be employed in the inventive method
contains
one or more of the following components: nitrocellulose, nitroglycerin,
ethylene glycol
dinitrate, one or more nitramines, RDX, nitroguanidines.
In one preferred embodiment, a humidified solvent-free raw explosive is used
as the raw
explosive material.
In an alternative embodiment, a solvent-dampened raw explosive is used as the
raw
explosive material. The solvent-dampened raw explosive preferably contains
acetone,
diethyl ether, ethanol or mixtures of the cited solvents.
In one embodiment, the raw explosive contains carbon in the form of carbon
black or
graphite, in particular at a volume of from 0.1 to 1.0 wt.%.
In a particularly preferred embodiment, the raw explosive contains carbon
nanotubes, in
particular at a volume of from 0.05 to 1.0 wt.%.
In addition to graphite, diamond and fullerenes, carbon nanotubes constitute
an allotopic
modification of carbon. In carbon nanotubes, graphite lattices are disposed in
tubular
form and capped on their ends by a fullerene half-cap structure.
The incorporating of carbon nanotubes leads to the following advantages for
the
explosives:
- Achieving an electrical conductivity or electrostatic dissipation (anti-
static) in the
otherwise insulating explosives
- Improving the mechanical properties, in particular as regards stability
- Increasing the thermal conductivity and the thermal stability of the
explosives
It has been shown that the inventive method is coupled with a number of
advantages. As
described above, isostatic pressing effects a gelling of the raw explosive
material. This
leads to clearly simplifying the subsequent post-gelation processing.
Employing a
shearing roller to effect gelling has in particular been shown to greatly
improve the initial
adhesion of the raw explosive to the roller as well as the heat transfer from
the roller to
the isostatically compressed raw explosive material. This enables less complex
shearing
devices to be used as well as shortens the process times, which leads to lower
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equipment costs and higher through-put. Shown to be an additional advantage is
that
the lower thermal loads on the material yielded by the shorter process times
leads to
increased long-term stability of the final product.
With respect to the simplifying of the shearing device, it has been shown that
the better
processing properties of the raw explosive material pre-treated by isostatic
pressing
enables the use of shorter shearing rollers, which in addition to lowering the
equipment
costs, also has the additional advantage of lower roller deflection, which
manifests itself
in less wear on the shearing device and increased process safety when
processing raw
explosive materials.
A further surprising advantage of the method according to the invention
comprises the
potential of processing raw explosives which could not be processed, or only
with great
difficulty, according to prior methods. For instance, pursuant the prior
methods, raw
nitro-cellulose and nitroglycerin / ethylene glycol dinitrate-based explosives
could only be
processed for certain compounds when the nitrocellulose had a specific
nitrogen content
(degree of nitration). Outside of this "window," conventional methods cannot
effect
gelation of the raw explosive. With the preceding step of isostatic pressing,
the inventive
method also enables the gelation of such raw explosives outside of this
window. This
considerably increases the flexibility of the procedure in terms of using
nitrocellulose of
differing nitrogen contents.
The following will draw on embodiments, illustrated by means of images, in
describing in
the invention in greater detail.
Example 1: SEM image analysis of an explosive material treated by means of
isostatic
pressing
A raw nitrocellulose/nitroglycerin explosive material underwent isostatic
pressing for 5
minutes at 80 C and 3500 bar.
Samples of the raw explosive material were taken prior to and subsequent the
isostatic
pressing and were thereafter analyzed using a scanning electron microscope.
Figure 2 shows the raw explosive material prior to the isostatic pressure
treatment while
Fig. 3 shows the raw explosive material after isostatic pressing. Noticeable
differences
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are seen in the structure of the raw explosive material prior to and
subsequent the
isostatic pressing. Seen in particular is almost a doubling in the volume of
nitrocellulose
fibers after the isostatic pressing step. The swelling suggests that the
gelling agent has
already partially dissolved the nitrocellulose chain association.
Example 2: Manufacturing an explosive
A raw explosive material (37% nitrocellulose, 37% nitroglycerin, 1% Centralit,
25% RDX)
is filled into a polyethylene tube. After evacuating the tube, it was sealed
and inserted
into the isostatic press. The temperature of the hydraulic fluid was at 85 C,
the pressure
applied was 5000 bar and the dwell time was 8 minutes. After extracting and
removing
from the mold, the formed body was dispensed to a shearing roller via a heated
comminution/metering device such that no cooling occurred.
It was shown that the raw explosive material pretreated by isostatic pressing
as
described above exhibits excellent properties for its further processing on
the shearing
roller.
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