Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Powder for accelerating projectiles for mortar systems
Technical Field
The invention relates to a powder as propulsion powder or ignition powder for
accelerating
projectiles for mortar systems, which is based on nitrocellulose and comprises
a crystalline,
nitramine-based energetic material at 1-30 wt% and an inorganic muzzle flash
suppressor, the
powder being present in the form of grains, and the grains on their surface
optionally having an
inert plasticizing additive. The invention further relates to a method for
producing such a powder.
Prior Art
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Within recent years there has been a significant shift in the area of large-
caliber barrel weapons.
Thus, up until the end of the Cold War, large-caliber tank and artillery
systems formed the
backbone of land-based units. These systems were optimized for the defence of
home territory, and
had a mobility limited by their great weight. In particular, weapons systems
of these kinds were not
transportable by air, a factor which greatly hindered rapid territorial
movement.
The outbreak of the 1st Iraq conflict at the beginning of the nineteen-
nineties, however, hailed a
marked turn away from the existing deployment scenarios. Large-caliber barrel
weapons had to be
transported to the site of deployment over long distances within a short time.
The 1st Iraq war
therefore marked the rediscovery of mortar systems. On account of their
relatively low weight,
large-caliber barrel weapons of this kind can easily be transported by air in
large numbers and
therefore are rapidly deployable in the event of conflict. Thanks to the
appearance of
high-performance electronics, moreover, such as satellite navigation or
guidance to target, massive
improvements were possible in precision.
The recent past has shown, then, that this mobility trend is being endorsed by
forces around the
globe. By virtue of the great interest in mortar systems, there has been an
increase in demand and, in
tandem therewith, an increase in the desire for power boosting. The new mortar
grenades with
electronic guidance to target and with the possibility for precise spot
detonation thus have a higher
weight than the existing, standard grenades. This gave rise to the need for
power-boosted
propulsion, which compensates the effect of the greater weight on the range,
or is even able to
extend the range.
It has been found, moreover, that in the last twenty years, military conflicts
have been located
primarily in hot climate zones, such as in Iraq or in Afghanistan. The
propulsion systems used
hitherto largely contained nitroglycerine in order to achieve a high power
potential, and were not
designed for the high thermal load. It has been ascertained that important
internal-ballistic data such
as muzzle velocity and peak gas pressure are altered as a consequence of
months-long deployment
and storage in hot climate zones. The lower muzzle velocity leads to a
reduction in range and
therefore reduces the strike probability. In contrast, the gas pressure
increases by up to 50%, posing
a great safety risk on firing. The strong climatic heat exposure, furthermore,
has a strong adverse
effect on the chemical stability of a propulsion system, causing phenomena
including the more rapid
consumption of the stabilizer. Overall, therefore, conventional,
nitroglycerine-containing powders,
3
when stored in hot bunkers or below in munition crates under direct
insolation, pose a safety risk, in
that they may undergo a spontaneous transition to autocatalysis and may, by
exploding, injure
surrounding personnel and destroy buildings.
The Nitrochemie company recognized the signs of the times sonic while ago, and
commenced
development of a new generation of nitroglycerine-free high-performance
powders, which showed
no change in ballistic and chemical stability even in long deployments in hot
climate zones ¨ that is,
their use and storage in hot climate zones posed absolutely no safety risk.
This new powder
generation was first developed specifically for high-power applications in
medium-caliber barrel
weapons, such as some subcaliber APFSDS-T munitions or full-caliber airburst
munitions.
Weapons systems of these kinds are typically equipped with relatively long
barrels, and relatively
high peak gas pressures occur on firing, typically of 3000-5000 bar.
In contrast to these, the barrels in mortar systems are much shorter and the
peak gas pressures that
result on firing are lower, viz, lower by 1000 bar at maximum charge, and
lower correspondingly at
lower charges. This means that the power is still required to undergo
sufficient conversion even at a
few 100 bar gas pressure. This criterion was impossible to achieve with the
original
nitroglycerine-free high-power formulations. Consequently there was a need for
a new approach to
an appropriate propulsion technology, designed for the specific conditions of
mortar systems with
low peak gas pressures and short weapons tubes. Likewise required of a new
propulsion system of
this kind is excellent chemical and ballistic stability, the propulsion system
being required at the
same time to exhibit the property of undergoing conversion in mortar systems
with a high power
yield.
Description of the Invention
It is an object of the invention to create a powder belonging to the technical
field identified at the
outset, as propulsion powder or ignition powder for accelerating projectiles
for mortar systems, that
exhibits excellent chemical and ballistic stability and can be converted with
a high power yield.
In one aspect, there is provided a powder, as propulsion powder or ignition
powder for accelerating
projectiles for mortar systems, which is based on nitrocellulose and comprises
a crystalline,
nitramine based energetic material at 1-30 wt% and an inorganic muzzle flash
suppressor, the
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powder being present in the form of grains, and the grains having on their
surface an inert
plasticizing additive, wherein the inorganic muzzle flash suppressor is
present at 0.1-10 wt% and
the inert plasticizing additive is present at 0.01 to I wt%, wherein the inert
plasticizing additive is
camphor.
In another aspect, there is provided a method for producing a powder described
in the preceding
paragraph. A solvent-containing powder dough based on nitrocellulose and on a
crystalline,
nitramine-based energetic material at 1-30 wt%, and on an inorganic muzzle
flash suppressor at 0.1
wt%, is produced. A green grain is produced by extrusion of the solvent-
containing powder
dough. The solvent is removed from the green grain. The green grain is surface-
treated with 0.01 to
10 1 wt% of camphor as an inert plasticizing additive, and the surface-
treated green grain is dried.
An embodiment disclosed in the present disclosure relates to a powder, as
propulsion powder or
ignition powder for accelerating projectiles for mortar systems, which is
based on nitrocellulose.
The powder comprises a crystalline,
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nitramine-based energetic material at 1-30 wt% and an inorganic muzzle flash
suppressor at 0.1-10
wt%. The powder is present in the form of grains. The grains may have an inert
plasticizing additive
on their surface. This additive is present at not more than 1 wt%, i..e, in a
range of 0-1 wt%.
The grains preferably have an inert plasticizing additive on their surface at
0.01-1 wt%.
It is surprising that through the use of relatively small amounts of an inert
plasticizing additive on
the surface of the powder, it is possible to lower the pressure dependency at
increasing
temperatures. Thus it is known with regard to the propulsion powders for
medium-caliber
applications that with substantial amounts of an inert plasticizing additive,
the pressure profile can
be made flatter. Virtually no effects are achievable at less than 2 wt%. It
has nevertheless emerged
that this relationship does not apply to propulsion powders for mortar
applications. In the case of the
propulsion systems of the invention for mortar systems, a flat pressure
profile is achieved with
relatively small quantities of an inert plasticizing additive. If the
concentration is increased, the
pressure profile steepens gradually, and at a level of addition of markedly
more than 1 wt%, there is
a significant increase in the pressure with increasing temperature. In the
preferred range of not more
than 1 wt% of the inert plasticizing additive, the increase in the muzzle
velocity with increasing
temperature is also relatively small, and so the propulsion system is
distinguished overall by a
largely neutral temperature characteristic. For certain applications,
moreover, no inert plasticizing
additive at all is needed.
With a flat pressure profile, the powder of the invention exhibits a high
degree of energetic
conversion, leading to a high internal-ballistic performance capacity.
Mortar systems are understood generally to be systems which have a relatively
short tube and are
fired at relatively steep angles. There are mortars ranging from a caliber of
37 mm (light mortars)
up to 240 mm (ultra-heavy mortars). The most important among them are the
heavy mortars in
calibers of 60-120mm. A particular focus of the invention is on the mortars or
the corresponding
propulsion systems for systems with calibers of 60 mm, 81 mm, and 120 mm.
Furthermore, the powders of the invention may also be used as ignition powders
for mortar
applications. An ignition powder is mounted in the shaft of a mortar grenade
and is needed to boost
the impulse of the initial pyrotechnic detonation and to transmit it to the
propulsion powder in the
surrounding increments (horse shoes). The composition of an ignition powder is
identical to the
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composition of a propulsion powder. The powders, however, may differ in grain
dimension and in
grain geometry.
Both the propulsion powder and the ignition powder are extrudable bulk powders
which can be
produced in a solvent process and comprise nitrocellulose as their main
component. For more than a
5 hundred years, nitrocellulose has been the major starting material for
the production of monobasic,
diobasic, and tribasic propellent charge powders. It is obtained by nitration
of cellulose (cotton
linters), is available inexpensively in large quantities, and is offered with
a large spectrum of
different chemicophysical properties. Nitrocellulose varies, for example, in
its nitrogen content,
molecular weight, or viscosity, and on the basis of these differences can be
processed to the
different homogeneous propellent charge powder types. The energetic content of
nitrocellulose is
adjusted via the nitrogen content. In monobasic formulations, nitrocellulose
is the sole energetic
material, implying that the energy density of nitrocellulose is relatively
high by comparison with
other synthetic binder polymers.
The present powders are based on nitrocellulose. The latter preferably has an
average nitrogen
.. content of 12.6% ¨ 13.25%. The further key components present in the grain
matrix are a crystalline
energetic material and also an inorganic muzzle flash suppressor.
The crystalline energetic material raises the energetic content of the powder
and is used at a
concentration in the range of 1 ¨ 30wt%. At these proportions, in a base of
nitrocellulose, the
average distances between the individual crystals of the crystalline energetic
material are
.. sufficiently large that predominantly the individual crystals do not make
contact. As a result, on
exposure to external mechanical stimuli, the shock pulse cannot be passed on
from one crystal of
explosive to the adjacently situated crystals. Accordingly, a primary-acting
shock pulse is not
multiplied and transmitted throughout the powder volume. At higher weight
proportions of
crystalline energetic material, in contrast, the individual crystals,
considered statistically, are located
too close together, and this results in a sharp rise in the vulnerability of
the powder.
The inorganic muzzle flash suppressor is used at a concentration in the range
of 0.1 ¨ 1 Owt%.
Adding an inorganic muzzle flash suppressor suppresses the reaction of
uncombusted gases such as
hydrogen or carbon monoxide in the region of the weapon muzzle, meaning that
these gases do not
ignite or ignite only to a much lesser extent. Accordingly, the muzzle flash
is reduced, thereby on
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the one hand reducing the blinding effect of the fire on the gunner and also
making it more difficult
for the gunner to be located.
The crystalline, nitramine-based energetic material preferably comprises at
least one compound
from the group encompassing hexogen (RDX) and octogen (HMX). These two
compounds, of the
general formula R-N-NO2 (R = radical), have a relatively small radical R,
which constitutes a small
proportion of the overall molecule by comparison with the nitramine structural
element. As a result,
the two compounds have a relatively high energy content.
Preference is given to using RDX as crystalline energetic material. In
comparison to HMX, it is
more favorable and safe to produce. HMX is more expensive than RDX, but offers
no particular
advantages. Other nitramine compounds (e.g., NIGU, etc.) have relatively
little power in
comparison to RDX. For the purpose of stabilization it is also possible to use
conventional active
ingredients such as akardite II, for example.
With particular preference the crystalline nitramine compound has a defined
average grain size.
Thus, for example RDX preferably with an average grain size of 4 - 8
micrometers, more
particularly 6 micrometers, is used. The homogeneous particle size of the
crystalline energetic
material permits powders to be produced that have relatively consistent
chemical and ballistic
properties.
Alternatively to the nitramine compounds, a nitrate ester of the general
formula R-O-NO2, for
example, would also be conceivable. In comparison to nitramine compounds,
though, nitrate esters
are less chemically stable. It is also possible to use at least one of the
following compounds as
crystalline nitramine compounds: hexanitroisowurtzitane (CL-20, CAS -# 14913-
74-7),
nitroguanidine (NIGU, NQ, CAS- # 70-25-7, N-metylnitramine (tetryl, N-methyl-
N,2,4,6-
tetranitrobenzolamine, CAS-# 479-45-8), and also nitrotriazolone (NTO, CASH
932-64-9) and
triaminotrinitrobenzole (TATB, CASH 3058-38-6). All of these energetic
compounds can be used
.. individually or in combination with one another.
The proportion of the crystalline energetic material is more preferably 5 - 25
wt%. Especially
favored are powders which have crystalline energetic materials in proportions
of 10 - 20 wt%. At
weight proportions of below 25 wt%, more particularly down to 20 wt%, the
distances between the
individual crystals of the energetic material are such that the vulnerability
of the powder lies at a
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very low level. The use of an inert plasticizing additive may attenuate the
vulnerability of the
powder somewhat in the event of a relatively high weight proportion of the
crystalline nitramine
compound. As a result it is easily possible to use high proportions of the
crystalline nitramine
compound.
In addition to its property as a crystalline energetic material, RDX also has
certain stabilizing
properties, which are manifested from as little as around 1 wt% and which rise
only insignificantly
as the proportion increases.
The inorganic muzzle flash suppressor preferably comprises at least one
compound from the group
of the alkali metal salts such as potassium nitrate and potassium sulfate, for
example. As well as
reducing muzzle flash, these compounds may also accelerate burn-off and
thereby reduce the
formation of residues, thereby further increasing the degree of energetic
conversion.
In one particular embodiment, the inorganic muzzle flash suppressor is present
in a proportion of
0.1 - 5 wt%.
The inert plasticizing additive which may be located on the surface of the
powder grain comprises,
in particular, at least one compound from the group encompassing camphor,
dialkyl phthalates
(preferably di-(C8-C12) phthalates or hydrogenated derivatives thereof), and
dialkyldiphenylureas
(preferably dimethyldiphenylurea, known under the trivial name centralite II).
The inert plasticizing
additive may also be applied as a combination of two or more individual
compounds.
The particularly preferred compound applied optionally to the surface of the
powder grain is
camphor.
Moreover, the surface of the powder grain is treated preferably with graphite
and ethanol.
The extruded powder grains are preferably subjected to a surface treatment
with ethanol and
graphite. Optionally the surface is treated with an inert plasticizing
additive. The inert plasticizing
additive penetrates the near-surface zones of the powder grain, where it
remains ¨ that is, it is
localized and is not distributed in the grain matrix. The inert plasticizing
additive has a depth of
penetration of a few 100 micrometers, e.g., at most 400 micrometers,
preferably 100 ¨ 300
micrometers. This means that at least 95 wt% of the inert plasticizing
additive is present down to
that depth.
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The applied graphite remains preferably at the surface of the powder grain.
The effect on the properties of the powder grain of the surface treatment,
i.e., of the application of
ethanol and graphite and optionally of the inert plasticizing additive to the
surface of the extruded
powder grain, is positive. For instance, a temperature-neutral behavior and
the bulk density (i.e., the
amount of powder that can fit within a given container volume) are improved in
particular through
surface treatment with graphite and ethanol. The pressure level (i.e., the
ratio of peak gas pressure
to muzzle velocity) is improved particularly through the addition of the inert
plasticizing additive to
the surface of the extruded powder grain, although this may impair the
temperature coefficient. At
the same time, the grain matrix no longer necessarily includes inert
compounds, and is able
consequently to have the maximum possible amount of energetic compounds. The
maximum effect
can be achieved through a surface treatment with a combination of these
substances.
In the case of powders for mortar applications, the inert plasticizing
additive is more preferably
present on the surface of the grain at not more than 0.1 wt%, i.e., at 0-0.1
wt%, more particularly in
a range of 0.01-0.1 wt%. At these specific amounts of the inert plasticizing
additive, the change in
the muzzle velocity and also the pressure increase on transition to high
temperatures is relatively
small. With significantly larger quantities of the inert plasticizing
additive, the possibility of
achieving temperature-neutral behavior goes down.
The grains for propulsion preferably have a circular-cylindrical geometry with
lengthwise channels
in the axial direction. The number of channels is arbitrary; a grain often has
one channel, or 7 or 19
channels. A propellent charge powder of this kind, also called hole powder, is
consequently
pourable and free-flowable, and can therefore be filled industrially into
cartridges.
The ratio of length (L) to diameter (D) of the cylindrical grain typically has
a value L/D = 0.25 ¨ 5.
The length of the circular cylinder is in the range, for example, of 0.3 ¨ 10
mm, and the diameter is
in the range of 0.3 ¨ 10 mm.
Where the invention is configured as multihole powder, preference is given to
a geometry with a
small pitch circle and therefore a relatively large outer wall thickness. This
means that, viewed in
cross section, the individual lengthwise channels are arranged more closely at
the center and occupy
overall a smaller pitch circle. Preferably, for example, six lengthwise
channels in a 7-hole powder
with a total cross section of about 3.6 mm form a pitch circle having a
diameter of about 2.1 mm.
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In one particular embodiment, the individual lengthwise channels of a
propulsion powder have a
hole diameter of 0.1 - 0.5 mm.
Where the powders of the invention are used as ignition powders, the grain
dimensions are typically
smaller than in the context of propulsion applications. Moreover, they
frequently have a
circular-cylindrical geometry with a central lengthwise channel. They have,
for example, an outside
diameter of 1.3-1.7 mm, a length of 1.5-2.0 mm, an average wall thickness of
0.6-0.8 mm, and a
hole diameter of about 0.10 mm.
Alternatively the material for the powders may be present in the form of
strips or may be extruded
directly into a defined form suitable for barrel weapons. In this form, it is
particularly suitable for
large-caliber munitions. This typically includes forms for which the width is
much smaller (e.g., at
least 5 times or at least 10 times) than the length, and the thickness in turn
is much smaller (e.g., at
least 5 times or at least 10 times) than the width. Typically the thickness
is, for example, 1-2 mm,
the width is, for example, 10 mm or more, and the length is, for example, 100¨
150 mm.)
Also conceivable are what are called shaped bodies, i.e., hollow-cylindrical
forms for a munition,
where the sleeve is absent and/or is replaced by the shaped body arranged
behind the ignition
system.
The grain matrix may optionally include further additions, known per se. For
stability increase it is
possible, for instance, for sodium hydrogen carbonate (CAS-4:144-55-8),
calcium carbonate (CAS-
4: 471-34-1), magnesium oxide (CAS-4: 1309-48-4), akardite II (CAS-4: 724-18-
5), centralite I
(CAS-4: 90-93-7), centralite 11 (CAS-4: 611-92-7), 2-nitrodiphenylamine (CAS-
4: 836-30-6) and
diphenylamine (CAS-4: 122-39-4) to be added. Additives such as, for instance,
lime, manganese
oxide, magnesium oxide (CAS-4: 1303-48-4), molybdenum trioxide (CAS-4: 1313-27-
5),
magnesium silicate (CAS-4: 14807-96-6), calcium carbonate (CAS-4: 471-34-1),
titanium dioxide
(CAS-4: 13463-67-7), tungsten trioxide (CAS-4: 1314-35-8) serve for tube
relief; compounds such
as phthalic esters, citric esters, or adipic esters are customary
plasticizers.
Furthermore, the green grain, in other words the powder still untreated per
se, in the matrix may
also include further known additions, for improving the ignition behavior and
for modulating the
burn-off behavior, for example.
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A method for producing a powder of the invention is distinguished by the fact
that a
solvent-containing powder dough based on nitrocellulose and on a crystalline,
nitramine-based
energetic material at 1-30 wt%, and on an inorganic muzzle flash suppressor is
produced.
Subsequently, a green grain is produced from this solvent-containing powder
dough by extrusion.
5 The solvent is removed from this green grain, and the green grain is
optionally surface-treated with
an inert plasticizing additive. Finally, the optionally surface-treated green
grain is dried.
A powder of the invention whose binder consists primarily of nitrocellulose
and which additionally
comprises a crystalline, nitramine-based energetic material and an inorganic
muzzle flash
suppressor can be produced on existing manufacturing plants. The solid
components of the
10 .. formulation can be admixed with a solvent mixture, for example. The
resulting solvent-moist
kneading dough can be kneaded in a kneeder and then extruded in a press to the
desired geometry.
The extrudates can be subjected to preliminary drying and cut to the desired
grain length. Then the
solvent may be withdrawn from the grain. The grain may then optionally be
surface-treated with an
inert plasticizing additive and/or subjected to a finishing operation.
.. The green grain is preferably surface-treated with ethanol and graphite,
i.e., graphitized.
Graphitizing may be carried out as an individual method step. It is also
possible, however, to apply
graphite and ethanol together with the inert plasticizing additive to the
green grain.
With particular preference the solvent is removed from the green grain by way
of a humid air
method.
The green grain obtained by extrusion comprises an inorganic muzzle flash
suppressor in the grain
matrix. For the removal of the solvent from the grain matrix, accordingly, the
green grain ought not
to be subjected to a bath process, since otherwise the water-soluble inorganic
muzzle flash
suppressor would be washed out of the grain matrix.
The solvent which has been used in the production process is therefore removed
by means of humid
air methods. In this case the solvent-moist green grain has a stream of air
passed through it for 10 ¨
60 hours, this stream of air being at temperatures between 20 ¨ 70 C, being
saturated with water
vapor, and flowing at high rates of several hundred m3 per hour. In this way
the proportion of the
solvent is reduced to <1%, while the water-soluble muzzle flash suppressor is
not removed from the
grain matrix, but instead remains therein.
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After the surface-treated grain has been dried, it is preferable for finishing
to take place. Finishing
refers in particular to the careful drying and screening of the surface-
treated grain.
Further advantageous embodiments and combinations of features of the invention
will become
apparent from the detailed description below and from the entirety of the
patent claims.
Ways of Implemeting the Invention
During the production of the green grain, various additions are added to the
nitrocellulose-based
powder dough; in order words, the additions are distributed uniformaly within
the matrix. The total
= amount of these additions, with the exception of the crystalline
nitramine compound, is 0-10 wt%
relative to the nitrocellulose, preferably 2-7 wt%. The total amount of the
crystalline nitramine
compound, which is typically RDX, is 0-30 wt% of the amount of nitrocellulose,
preferably 0-20
wt%. The crystalline nitramine compound may have to be subjected to pre-
treatment before it is
added to the powder dough, in order to improve attachment to the matrix.
After the kneading of the powder dough with solvents, the green grain is
extruded through a die.
Subsequently the water and the solvent are removed, preferably by means of
humid air drying. The
green grain is subjected to a surface treatment, in which, for example,
optionally, an inert
plasticizing additive and preferably further additives such as graphite, for
example, are applied in
the presence of ethanol (impregnation + coating).
Example 1 ¨Propulsion powder 1 (FM 4651/21)
For the production of 520 kg of a 7-hole powder, 20 wt% of RDX, 1.2 wt% of
akardite II, and 3.2
wt% of potassium nitrate and nitrocellulose with a nitrogen content of 13.20
wt% (balance to 100
wt%) are processed to a solvent-moist kneading dough, with addition of diethyl
ether and ethanol,
over 70 minutes. The powder dough is subsequently pressed through a die (i.e.,
extruded) with a
7-hole geometry and a 5.2 mm strand cross section. The extruded strands are
briefly subjected to
preliminary drying in air, then cut to the desired length, and the resulting
green grain is laid out
evenly on fine-mesh screens. The green grain thereafter is subjected for 30
hours to a
water-saturated air flow of 200 m3/h and a temperature of 30 C and
subsequently for 30 hours to a
400 m3/h air flow and a temperature of 65 C (humid air drying). 60 kg of the
green grain heated to
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60 C are subsequently admixed, in a copper polishing drum heated to 55 C, with
0.05wt% of
graphite and 1.2 litres of ethanol, which are allowed to act thereafter for
one hour with continual
turning. Finally, the powder is spread out on metal sheets and dried at 60 C
for 24 hours.
The resulting propulsion powder 1 with the designation FM 4651/21 has the
following physical
properties: 3.63 mm outside diameter, 3.61 mm length, 0.76 mm average wall
thickness, and 0.20
mm hole diameter, 4251 J/g heat capacity and 1048 g/1 bulk density. Chemical
stability:
deflagration temperature = 172 C. STANAG 4582 heat flux calorimetry = 44 J/g
and 30.4 uW
(requirement according to STANAG 4582 standard: maximum heat evolution <114
W).
Example 2 ¨Propulsion powder 2 (FM 4650/22)
A powder dough according to example 1 is pressed through a die (i.e.,
extruded) with 7-hole
geometry and 4.8 mm strand cross section. The extruded strands are briefly
subjected to preliminary
drying in air and cut to the desired length, and the resulting green grain is
subjected to humid air
drying (as described in example 1). Then 60 kg of the green grain are
preheated to 60 C and
transferred into a copper polishing drum which is heated at 55 C. The green
grain is admixed with
0.05% graphite and with a solution of 1 wt% of camphor in 1.2 kg of ethanol,
and turned
continually for one hour. Finally, the powder is spread out on metal sheets
and dried at 60 C for 24
hours.
The resulting propulsion powder 2 with the designation FM 4650/22 has the
following physical
properties: 3.42 mm outside diameter, 3.45 mm length, 0.71 mm average wall
thickness, and 0.19
mm hole diameter, 4152 J/g heat capacity and 1002 g/1 bulk density. Chemical
stability:
deflagration temperature = 172 C. STANAG 4582 heat flux calorimetry = 47 J/g
and 30.9 ttW
(requirement according to STANAG 4582 standard: maximum heat evolution <114
ttW).
Comparison of Propulsion powders 1 and 2
Comparison of the pressure increase at high powder temperatures through
variation in the amount
of camphor
System: 120 mm pressure barrel with identical internal-ballistic
characteristics to the 120 mm
standard mortar M120 of the U.S. forces, particularly in relation to tube
length and muzzle
geometry. The projectile mass of the inert mortar grenades used was 15.5 kg.
Velocity was
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measured by Doppler radar, and the peak gas pressure was detected
piezoelectronically in the region
of the muzzle. The results of the temperature firings of the two propulsion
powders, with 0 wt% and
1 wt% camphor coating, carried out at powder temperatures of 21 C and 63 C,
are compiled in
Tables 1 and 2 below.
Table 1
FM 4651/21 0 wt% camphor
Charge mass Powder Velocity Peak gas Pressure Pressure
[g] temperature [m/s] pressure [psi] increase [psi] change
[%]
[ C]
740 21 369.0 18224
2458 13
740 63 378.5 20682
Table 2
FM 4650/22 1 wt% camphor
Charge mass Powder Velocity Peak gas Pressure Pressure
[g] temperature [m/s] pressure [psi] increase [psi] change
[%]
[ C]
740 21 366.1 17494
4015 23
740 . 63 376.3 21509
The results in Tables 1 and 2 show that the pressure increase on transition
from 21 C to 63 C is
much less high with the propulsion powder 1 (FM 4651/21) with 0 wt% camphor
than in the case of
propulsion powder 2 (FM 4650/22) with 1 wt% camphor. This finding is
surprising and goes
against the previous experience in the medium-caliber area, according to which
the increase in
pressure can be lowered by an increase in the amount of camphor.
Example 3 ¨ Propulsion powder 3 (FM 4714)
A powder dough according to example 1 is extruded through a die with 7-hole
geometry and
5.1 mm strand cross section. The extruded strands are briefly subjected to
preliminary drying in air
and cut to the desired length, and the resulting green grain is subjected to
humid air drying (as
described in example 1). Then 120 kg of the green grain are preheated to 60 C
and transferred into a
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copper polishing drum which is heated at 55 C. The green grain is admixed with
0.05% of graphite
and with a solution of 0.1 wt% of camphor in 2.4 kg of ethanol, and turned
continually for one hour.
Finally, the powder is spread out on metal sheets and dried at 60 C for 24
hours.
The resulting propulsion powder 3 with the designation FM 4714 has the
following physical
properties: 3.58 mm outside diameter, 3.59 mm length, 0.75 mm average wall
thickness, and
0.20 mm hole diameter, 4269 J/g heat capacity and 1026 g/1 bulk density.
Chemical stability:
deflagration temperature -= 172 C. STANAG 4582 heat flux calorimetry = 50 Jig
and 32.6 ttW
(requirement according to STANAG 4582 standard: maximum heat evolution <114
").
Comparison of Propulsion powder 3 with a ball powder
Comparison of the pressure increase at high powder temperatures and the
ballistic performance with
nitroglycerine-containing comparison powder (GD St Marks ball powder)
System: 120 mm pressure barrel with identical internal-ballistic
characteristics to the 120 mm
standard mortar M120 of the U.S. forces, particularly in relation to tube
length and muzzle
geometry. The projectile mass of the inert mortar grenades used was 15.1 kg.
Velocity was
measured by Doppler radar, and the peak gas pressure was detected piezo
electronically in the
region of the muzzle. The results of the temperature firings of the two powder
types, carried out at
powder temperatures of 21 C and 63 C, are compiled in Tables 3 and 4 below.
Table 3
FM 4714 0.1 wt% camphor
Charge mass Powder Velocity Peak gas Pressure Pressure
[g] temperature [m/s] pressure [psi] increase [psi] change
[%]
[ C]
728 21 373.5 18643
2013 11
728 63 378.5 20656
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Table 4
Comparison Powder > lOwt% Nitroglycerine
Charge mass Powder Velocity Peak gas Pressure
Pressure
[g] temperature [m/s] pressure [psi] increase [psi] change
[%]
[ C]
756 21 349.4 14659
2261 15
756 63 362.1 16920
The results in Tables 3 and 4 show that in the case of the nitroglycerine-
containing comparison
5 powder, the pressure increase on transition to 63 C is much higher than
for propulsion powder 3
(FM 4714) with 0.1 wt% camphor. Moreover, the velocity of the comparison
powder at 21 C, in
spite of a charge mass 28g higher, is about 25 m/s lower, thereby critically
reducing the range.
Overall, investigations on the powder of Example 3 show that this is a powder
having a better
performance with a low temperature dependency. Moreover, the scatter in
individual measurements
10 is much less than for the other powders, pointing to a very homogeneous
powder which is therefore
consistent in its performance.
Example 4 ¨ Ignition Powder 1 (FM 4483/21)
A powder dough according to example 1 is pressed through a die (i.e. extruded)
with 1-hole
geometry and 2.1 mm strand cross section. The extruded strands are briefly
subjected to preliminary
15 drying in air and cut to the desired length, and the resulting green
grain is subjected to humid air
drying (as described in example 1). Then 20 kg of the green grain are
preheated to 60 C and
transferred into a copper polishing drum which is heated at 55 C. The green
grain is admixed with
0.3 wt% of graphite and with 0.3 kg of ethanol, after which it is left for one
hour with continual
turning. Finally, the powder is spread out on metal sheets and dried at 60 C
for 24 hours.
The resulting ignition powder 1 with the designation FM 4483/21 has the
following physical
properties: 1.47 mm outside diameter, 1.75 mm length, 0.69 mm average wall
thickness, and 0.10
mm hole diameter, 4393 J/g heat capacity and 1001 g/1 bulk density. Chemical
stability:
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deflagration temperature = 172 C. STANAG 4582 heat flux calorimetry = 46 J/g
and 30.2
(requirement according to STANAG 4582 standard: maximum heat evolution <114
1.1,W).
Example 5 ¨ Ignition Powder 2 (FM 4483/22)
A powder dough according to example 1 is pressed through a die (i.e. extruded)
with 1-hole
geometry and 2.1 mm strand cross section. The extruded strands are briefly
subjected to preliminary
drying in air and cut to the desired length, and the resulting green grain is
subjected to humid air
drying (as described in example 1). Then 20 kg of the green grain are
preheated to 60 C and
transferred into a copper polishing drum which is heated at 55 C. The green
grain is admixed with
0.3 wt% of graphite, 0.5 wt% of camphor, and 0.15 kg of ethanol, after which
it is left therein for
one hour with continual turning. Finally, the powder is spread out on metal
sheets and dried at 60 C
for 24 hours.
The resulting ignition powder 2 with the designation FM 4483/22 has the
following physical
properties: 1.47 mm outside diameter, 1.75 mm length, 0.69 mm average wall
thickness, and 0.10
mm hole diameter, 4343 J/g heat capacity and 995 g/1 bulk density. Chemical
stability: deflagration
temperature = 172 C. STANAG 4582 heat flux calorimetry = 52 J/g and 32.4 laW
(requirement
according to STANAG 4582 standard: maximum heat evolution <114 OW).
Comparison of Ignition powders 1 and 2 with a ball powder
Comparison of the pressure increase at high powder temperatures through
variation in the amount
of camphor in ignition powders 1 and 2, and comparison with imported M48 ball
powder.
System: 120 mm pressure barrel with identical internal-ballistic
characteristics to the 120 mm
standard mortar M120 of the U.S. forces, particularly in relation to tube
length and muzzle
geometry. The projectile mass of the inert mortar grenades used was 14.0 kg.
Velocity was
measured by Doppler radar, and the peak gas pressure was detected piezo
electronically in the
region of the muzzle. The test was carried out with charge 4, i.e.; using four
M234 standard
increments. The results of the temperature firings of the two powders with
camphor coatings of 0
wt% (FM4483/21) and 0.5 wt% (FM4483/22) in comparison to the imported M48 ball
powder in
the standard M1020 detonation cartridge, carried out at powder temperatures of
21 C and 63 C, are
compiled in Tables 5, 6, and 7 below.
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Table 5
FM 4483/21 0 wt% camphor
Charge mass Powder Velocity Peak gas Pressure Temperature
[g] temperature [m/s] pressure [psi] increase [psi]
coefficient
[ C]
60.9 21 320.9 13150
1708 1.13
60.9 63 328.8 14858
Table 6
FM 4483/22 0.5 wt% camphor
Charge mass Powder Velocity Peak gas Pressure Temperature
[g] temperature [m/s] pressure [psi] increase [psi]
coefficient
[ C]
62.8 21 318.5 12139
1933 1.16
62.8 63 326.4 14072
Table 7
M48 ball powder
Powder Velocity Peak gas Pressure Temperature
temperature [m/s] pressure [psi] increase [psi] coefficient
[ C]
21 322.4 13650
2284 1.17
63 329.7 15934
It is apparent that the presence of 0.5 wt% of camphor in the inventive
ignition powder 2 reduces
the peak gas pressure at 21 C, which may be advantageous for certain
applications. However,
ignition powder 2 with 0.5 vvt% of camphor exhibits a higher pressure increase
than that without
camphor. Depending on application, therefore, a precise weighing of the
optimum amount of
camphor must be made, in order to allow the system requirements dictated by
the application to be
fulfilled in the best-possible way. It is further found that in the case of
the imported M48 ball
powder the highest gas pressure results at 21 C. For the imported ball powder
M48, the pressure
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increase from 21 C to 63 C, at about 2300 psi, is much higher in comparison to
the two inventive
ignition powders 1 and 2.
In summary it can be stated that the nitrocellulose-containing powders of the
invention, as
propulsion powders or ignition powders, which comprise a crystalline,
nitramine-based energetic
material and an inorganic muzzle flash suppressor, and which have small
amounts of an inert
plasticizing additive on the surface, are suitable for accelerating
projectiles for mortar systems, at
the same time exhibiting a temperature-independent behavior and therefore
being suitable for use
independently of climatic conditions.
