U.S. patent application number 11/358049 was filed with the patent office on 2006-11-30 for method for producing a propellant.
This patent application is currently assigned to Nitrochemie Wimmis AG. Invention is credited to Markus Fahrni, Alexander Huber, Ulrike Jeck-Prosch, Bruno Ossola, Kurt Ryf, Alfred Steinmann, Beat Vogelsanger.
Application Number | 20060266451 11/358049 |
Document ID | / |
Family ID | 8183789 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266451 |
Kind Code |
A1 |
Fahrni; Markus ; et
al. |
November 30, 2006 |
Method for producing a propellant
Abstract
The proposed propellant powder exhibits a
temperature-independent burning behavior and high ballistic
stability. The production process starts with a perforated bulk
powder grain, which is processed inside a mixing apparatus with a
solid material, a plug-stabilizing moderator or deterrent (if
necessary also a radical initiator) and a low-viscous liquid. With
a minimum amount of solid material, moderator or deterrent and
liquid and because of the continuous mixing, the form function is
influenced in such a way that the gas-formation rate is practically
independent of the propellant powder temperature. As a result, the
muzzle energy at the normal temperature and, above all, at a low
deployment temperature can be increased markedly as compared to
that of a standard propellant powder. With the propellant powder
according to the invention, for which the grain has at least one
perforation that discharges with an opening to the outside surface
of the grain, wherein the opening is closed off with a plug, the
plug has a temperature-dependent mobility. As a result, the plug
has a higher mobility for a lower deployment temperature than for a
higher deployment temperature, so that the plug permits a faster
hole burning at a lower deployment temperature than at a higher
deployment temperature.
Inventors: |
Fahrni; Markus;
(Laengenbuehl, CH) ; Vogelsanger; Beat; (Thun,
CH) ; Steinmann; Alfred; (Praroman, CH) ;
Ossola; Bruno; (Faulensee, CH) ; Jeck-Prosch;
Ulrike; (Muehldorf, DE) ; Huber; Alexander;
(Bruckmuehl, DE) ; Ryf; Kurt; (Wimmis,
CH) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Assignee: |
Nitrochemie Wimmis AG
Wimmis
CH
Nitrochemie Aschau GmbH
Aschau am Inn
DE
|
Family ID: |
8183789 |
Appl. No.: |
11/358049 |
Filed: |
February 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10096111 |
Mar 13, 2002 |
7051658 |
|
|
11358049 |
Feb 22, 2006 |
|
|
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Current U.S.
Class: |
149/2 |
Current CPC
Class: |
C06B 45/22 20130101;
C06B 21/0083 20130101; F42B 5/16 20130101 |
Class at
Publication: |
149/002 |
International
Class: |
C06B 45/00 20060101
C06B045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2001 |
EP |
01 810 255.8 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. A method for producing a propellant, wherein a grain is
produced with at least one hollow chamber that discharges with an
opening to the outside surface of the grain, characterized in that
a solid material in the form of a plug is inserted into the opening
in such a way that the plug has a temperature-dependent mobility,
meaning it has a higher mobility at a lower deployment temperature
than at a higher deployment temperature, so that the plug permits a
faster hole burning at a lower deployment temperature than at
higher deployment temperature.
24. A method according to claim 23, characterized in that the solid
material is inserted, compacted and anchored inside the opening
with the aid of a moderator, or a moderator that is not soluble in
the grain, as well as a highly volatile liquid.
25. A method according to claim 24, characterized in that the plug
is produced by processing the solid material, the moderator and the
liquid inside a mixing apparatus, at a temperature ranging from
0.degree. to 90.degree. C., over a treatment period of between 10
minutes and 3 hours and with a rotational speed of the mixing
apparatus of between 2 and 30 rotations per minute.
26. A method according to claim 25, characterized in that the solid
material and/or the moderator are added to the mixing apparatus in
an amount of 0.001 weight % to 4 weight %, relative to the weight
of the untreated grain.
27. A method according to claim 25, characterized in that the
low-viscous liquid is used in the mixing apparatus in amounts of
0.1 weight % to 5 weight %, relative to the weight of the untreated
grain.
28. A method according to claim 24, characterized in that graphite,
talcum, titanium oxide, carbon black, potassium sulfate, potassium
cryolite, calcium carbonate, wolfram trioxide is used as solid
material and that in particular polytetrahydrofuran, polyvinyl
alcohol, poly(vinylalcohol-co-vinylacetate),
poly(vinylalcohol-co-ethylene), polybutadienediol,
polybutadienediol dimethacrylate, poly(.alpha.-methylstyrene),
polybutadiene or polybutadienediol-diacrylate is used as
moderator.
29. A method according to claim 24, characterized in that water,
ethanol, hexane, cyclohexane or a mixture of water/ethanol,
water/methanol or water/acetone is used as liquid.
30. A method according to claim 24, characterized in that the
liquid is removed through evaporation from the opened, rotating
mixing apparatus and that the propellant subsequently is stored for
3 days at 60.degree. C.
Description
TECHNICAL FIELD
[0001] The invention relates to a propellant powder, for which the
grain has at least one perforation that discharges with an opening
to the outside surface of the grain, wherein this opening is closed
off with a plug. The invention furthermore relates to a method for
producing a propellant powder of this type.
PRIOR ART
[0002] Propellant powders (TLP) for conventional barrel weapon
systems should be configured such that they can function safely and
without problems under different environmental conditions
(system-specific factors). Great temperature differences during the
weapon deployment represent one of the most important influences,
which a propellant or ammunition manufacturer must take into
consideration. Thus, local and/or global climactic conditions may
require secure propulsion solutions for a temperature range of
between -54.degree. C. and +63.degree. C./+71.degree. C. (and up to
+100.degree. C. for the deployment from an aircraft).
[0003] Since propellant powders naturally burn
temperature-dependent (based on the laws of physics), considerable
pressure differences normally occur during the firing of weapons in
the aforementioned temperature range.
[0004] For all weapon systems as well as barrel weapons, there is a
constant demand for performance increases (e.g. higher kinetic
energy for the tank-fired projectile, longer ranges for artillery
shells, shorter flight times for anti-aircraft projectiles [machine
gun], higher first-hit probability, etc.).
[0005] Performance increases that must be realized with new
developments are extremely cost-intensive.
[0006] For cost reasons, interest is high in the field of weapon
technology to achieve the desired performance increases with
previously introduced, existing weapons platforms (increase in
combat effectiveness).
[0007] The desired performance increases can be achieved only
through utilizing all reserves and a combination of suitable
measures (optimizing of internal ballistic actions), wherein the
basic weapon-technological requirements remain unchanged.
[0008] These measures include: [0009] Achieving a higher efficiency
of the basic propellant powder formulation by using formulations
with a high force (specific energy or propellant force). [0010]
Achieving maximum bulk densities (through high densities or optimum
surface properties of the propellant powder) inside the
predetermined casing volumes. [0011] Increasing the progressiveness
of the propellant powder burning [0012] Minimizing or eliminating
the dependence of the propellant powder burning rate on the
temperature.
[0013] The problem with providing these desired new
high-performance propellant powders is that undesirable side
effects must be avoided. That is to say, the full expanded system
compatibility with respect to barrel (erosion, corrosion), weapon
(peak gas pressure) and environment (avoiding formulation
components that are problematic for the environment) must still be
ensured for the demanded, higher performance level.
[0014] Finally, it is desirable to produce these demanded
high-performance propellant powders cost-effectively, meaning with
easy to obtain, cheap starting materials and simple techniques.
[0015] According to the laws of physics, the burning speed depends
on the spontaneous ignition temperature and the starting
temperature of the propellant body. This relationship leads to the
well-known characteristic of such traditional propellant powders,
meaning that the linear burning speed more or less depends on the
starting temperature. From this, it necessarily follows that the
peak gas pressure and the muzzle velocity have a more or less steep
temperature gradient. The temperature-dependent performance of such
propellant powders has considerable disadvantages, for example a
low first hit probability and considerably lower projectile energy
during the deployment at normal and, above all, at low
temperatures. The limiting factor is always the peak gas pressure
occurring at high temperatures.
[0016] The relevant literature contains few works dealing with the
modification of weapon systems or propellant powders, which
modification results in uniform, temperature-independent
performances.
[0017] Thus, a surface coating is disclosed in U.S. Pat. No.
4,106,960, for which a three-base 19-hole propellant powder is
coated during 20 depositing and drying cycles with 18%
polymethylmethacrylate (mol weight>100'000), 3.4% titanium
oxide, 1.9% diphenyl-cresylphosphate and 100% toluene (all
percentages relative to the propellant powder). The propellant
powder is preferably coated with approximately 10 to 20 weight
shares (relative to the propellant powder amount) of inert
material. This corresponds to an inert cover layer of 100 to 200
microns. As a result, the propellant powder ignition is delayed
considerably. The temperature dependence of the propellant powder
can be inverted if this highly treated propellant powder is mixed
with an untreated propellant powder having a non-delayed ignition.
A mixture of treated grain and untreated grain tested in the
pressure bomb (where all material burns up) showed a
temperature-independent behavior, wherein the burning time was not
specified. The temperature-independent behavior was not tested in a
weapon firing.
[0018] An article providing an overview by D. L. Kruczynski, J. R.
Hewitt, "Technical Report BRL-TR-3283 (1991), mentions
temperature-compensation techniques and technologies where
deterrents are said to exert a certain influence on the reduction
of the temperature coefficient. However, the mechanism for this
appears to be unclear so far. Furthermore suggested is the
production of a propellant powder, which utilizes the brittle
fracture (surface area enlargement) at low firing temperatures for
an increase in the vivacity and the compression of the soft grain
and thus the holes (decreasing the surface area) at high firing
temperatures for a reduction in the vivacity. Processes of this
type, however, are hard to control and contain an immense safety
risk.
[0019] Another suggestion for reducing the temperature dependence
relates to adapting the cartridge chamber volume in dependence on
the propellant powder temperature.
[0020] A different publication that also deals with the reduction
in the temperature sensitivity of propellant powders, used in
particular for artillery weapons, and uses similar arguments is by
T. T. Nguyen, R. J. Spear, Department of Defense, Australia,
DSTO-TR-0102 (1994). It is noted in this publication that no
additive could be found to reduce the temperature dependence of the
propellant powder combustion.
REPRESENTATION OF THE INVENTION
[0021] It is the object of the invention to specify a propellant
powder of the aforementioned type, which exhibits a mostly
temperature-independent burning without resulting in noticeable
losses of other characteristics. In particular, this should not
result in a worsening of the ignition behavior or the chemical and
ballistic stability of the propellant powder.
[0022] This object is solved with the features in claim 1.
According to the invention, a propellant powder of the
aforementioned type is distinguished by the temperature-dependent
mobility of the plugs, which results in a higher mobility at a
lower deployment temperature than at a higher deployment
temperature. Thus, with a lower deployment temperature, the plugs
permit a stronger hole burning than at a higher deployment
temperature.
[0023] Plugs are formed inside the perforation tunnels with the aid
of a suitable surface treatment of perforated propellant grains. As
a result, the propellant grains processed in this way burn
practically independent of the propellant powder temperature. A
behavior of this type is referred to as SCDB.RTM..sup.1 effect.
[0024] The above effect is based on the temperature-dependent plug
mobility during the propellant powder ignition operation. If the
propellant powder temperature is high (resulting in a fast burning
speed), the plugs remain inside the perforation tunnels and a
minimum surface is available for the burning. With a low
temperature (slow burning speed),
[0025] the plugs are all removed by the ignition pressure wave and
a maximum surface area is available for the burning. Ideally, the
product of burning speed times the surface is constant for all
firing temperatures, which equals a temperature-independent
burning.
[0026] The temperature-dependent plug mobility is controlled by
fine-tuning the relevant parameters during the surface treatment
and by the temperature-dependent expansion of the propellant grain
matrix or the plug. Two important parameters in this connection are
the amount of graphite used and the treatment time. The longer the
treatment, the stronger the plugs. It must be taken into
consideration here that the introduction of graphite alone will not
generate the effect according to the invention. The graphite must
also be compacted or glued together to form a type of rigid body,
wherein solvents and deterrents are used for this. (If the grain is
soft, for example, a deterrent can also be omitted.)
[0027] In general, it is true that elastomeres, for example the
two-base or multi-base nitrocellulose, expand more or less
proportional to the increasing temperature above their glass
transition temperature (>-40.degree. C.).
[0028] The surface treatment for achieving a SCDB.RTM. effect is
normally realized at 30.degree. C. It means that the hole diameter
of such propellant grains is smaller at 63.degree. C. than at
30.degree. C. because of the material expansion. Since the plug
material inside the perforation tunnels also expands with
increasing temperature, these have a larger diameter at 63.degree.
C. Thus, the plugs are embedded securely at 63.degree. C. Added to
this is the fact that the propellant grains and also the plugs
(with the solid material being glued together with small amounts of
blasting oil and nitrocellulose) exhibit a higher adhesive behavior
at high temperatures. The plugs thus can hardly be displaced by the
pressure wave during the ignition.
[0029] With increasing burning (around the plugs), the plugs
gradually are slowly pushed into the hole inside by the enormous
gas pressure.
[0030] At a temperature of -40.degree. C., the hole diameters are
larger than at 30.degree. C. because of the contraction of the
grain material. The plug diameter decreases at this temperature
because of the material contraction. Thus, the plugs sit rather
loosely inside the perforation tunnels. The gluing effect of the
cold grain material is also reduced. The ignition shock
consequently drives the plugs immediately into the hole inside or
pulverizes these since the brittleness of the plugs that are
primarily composed of solid material clearly increases at low
temperatures.
[0031] Diverse parameters exist for the surface treatment according
to the invention (propellant powder composition and amount, amount
and grain size of the solid material, polarity and amount of
solvent, amount and polarity of deterrent or moderator, treatment
length and treatment temperature), which can be varied to adapt the
plug mobility. Thus, the mobility steadily decreases from the
lowest to the highest firing temperature.
[0032] It must be considered that the above-described plug mobility
in the perforation tunnels represents a statistic variable. Not
every plug reacts in the same way to the ignition pressure
wave.
[0033] The physical conditions existing with a low deployment
temperature ensure that the plugs will be pulled from their
positions during the first pressure wave already and thus free the
holes. The contact location between plugs and hole wall thus is
brittle so-to-speak at low temperature. With a higher temperature,
on the other hand, it is tough, so-to-speak, and can better resist
the ignition pressure wave. It must be taken into consideration
here that "brittleness" or "toughness" of the anchoring refers to
statistical parameters. It is not relevant that each plug reacts
exactly in the same way to the pressure wave. Rather, it is
sufficient if the totality of all plugs for all propellant grains
in the ammunition statistically exhibits the same characteristic
reaction. Of course, it is necessary to conduct tests within a
certain scope to achieve the desired temperature independence for a
specific ammunition. Based on the inventive statement on how to
select the mobility of the plugs, however, the person skilled in
the art can see which optimization should be made in the individual
case.
[0034] The hole burning characterizes to what degree the combustion
processes occurring inside the holes contribute to the gas
formation rate. The more holes are released, the more surface area
is available for the burning. Accordingly, the grain during each
time unit produces more gas.
[0035] It must be mentioned here that for the purpose of the
present invention, only the compacted and anchored portion of the
material inside the hole is understood to be the plug. The
relatively loose material underneath the compacted portion of the
filling does not function as plug within the meaning of this
invention and consequently is not called a plug. It is understood
that in practice there is not necessarily a clear boundary
delimiting the plug. The plug can also change in a "flowing" manner
over to the remaining portion of the filling inside the hole.
Insofar as the invention is concerned, however, there is always a
section with sufficiently high density, which can resist an
ignition pressure wave in a controlled manner.
[0036] The invention has diverse advantages as compared to the
approaches suggested in prior art. First of all, it must be noted
that the invention is basically suitable for double base and
multi-base perforated propellant powders deployed in barrel
weapons. Propellant powders can thus be produced, which have a
temperature-independent burning rate, can be initiated easily with
traditional ignition means and additionally have a high ballistic
stability (deployment service life). As a result of the temperature
independence (more or less uniform gas-formation rate), the
propellant powder energy can be used optimally over the complete
temperature range.
[0037] Tests have shown that by combining the internal ballistic
optimization and improvement measures, described in the following,
it is possible to achieve a performance increase (muzzle energy) of
10% and more for previously introduced weapon systems.
[0038] The plug should consist, if possible, of a substance that is
not soluble in the untreated grain (meaning the untreated
perforated propellant), thereby ensuring that the anchoring of the
plug inside the opening and thus the mobility of the plug cannot
change as a result of diffusion processes. The anchoring is
therefore essentially determined by the surface parameters in the
plane for the grain or plug structure.
[0039] The plug preferably consists essentially of an inert solid
material. Depending on the propellant powder temperature, the plug
is pushed more or less strongly into the perforation hole by the
pressure wave resulting from the ignition. The plug displacement
increases the active surface and, consequently, also the gas
development per unit of time. With a relatively low starting
temperature, the plug is quickly released from its anchoring. As a
result, the burnable propellant surface is increased all of a
sudden, so-to-speak. With a relatively high propellant powder
temperature, on the other hand, the anchoring of the plug is quite
resistant and the burnable propellant surface is reduced to a
minimum.
[0040] A solid material with a grain size in the range of 0.01 to
100 micrometers can be used, wherein the grain size should be
matched to the diameter of the perforation opening. If the grains
of the solid material are relatively large, they can be inserted
only with difficulty into the perforation opening. The grain size
typically will be in the range of 0.1 to 50 micrometers.
[0041] However, the solid material does not have to be inert; it
can also contain energy. Of course, it should ignite and burn
slower than the untreated grain.
[0042] Graphite, talcum, titanium oxide, carbon black, potassium
sulfate, potassium cryolite and/or calcium carbonate, for example,
are suitable as solid materials. However, other substances that do
not react with the untreated grain can be used as well. The
aforementioned substances can be used individually as well as in
combination.
[0043] The invention is not limited to a plug consisting
exclusively of inert substances. It is indeed possible to add small
amounts of an energetic solid material, in particular
nitrocellulose, hexogen, octogen, nitroguanidine, nitrotriazole,
ethylene dinitramine, ethyltetryl, ammonium picrate,
trinitrotoluene, trinitrobenzene, tetranitroaniline, and the like.
These can also include strong oxidants such as ammonium nitrate,
potassium nitrate, ammonium perchlorate, potassium perchlorate and
the like, provided these are not incompatible with the selected
mix. It must be ensured that the stability or resistance of the
plugs formed in the openings (perforations) to the ignition impulse
wave is not lost at higher propellant powder temperatures.
[0044] Compounds with a melting point above approximately
80.degree. C. are suitable energetic solid materials to be mixed
in. These solid materials should not have high sensitivity to
percussion or friction. A selection of highly-explosive substances
which thus have only limited suitability are listed in R. Meyer,
"EXPLOSIVSTOFFE" [Explosive Materials], Publishing House "CHEMIE"
[Chemistry] 1979, page 121 ff.
[0045] The plug preferably has a melting temperature that is above
the production temperature, storage temperature and/or deployment
temperature and, in particular, is above 90.degree. C.
[0046] The propellant typically is a double base or multi-base
single-hole or multiple-hole propellant. That is to say, the grain
is cylindrical (with an external diameter of, for example, 1 mm to
20 mm and preferably 3 mm to 15 mm) and is advantageously provided
with 7 to 19 holes extending through in axial direction. The ratio
of grain diameter to grain length is normally in the range of
0.3-2.0, preferably 0.8-1.2. The propellant geometry can also be
different; for example it can have a rosette shape or a hexagonal
shape.
[0047] The diameter for the holes is in the range of 0.03 to 0.5
mm, for example, and in particular in the range of 0.1 to 0.3 mm.
For the purpose of this invention, smaller holes are advantageous
because smaller amounts of inert material can be used in that case.
In addition, they allow for a better control of the quality of the
plug anchoring. The dense (compacted) plugs typically have a ratio
of length to diameter in the range of 5 to 60.
[0048] The untreated grain can be produced in a manner known per se
by compressing a solvent-containing or solvent-free propellant
powder dough or propellant powder pack with or without the additive
of blasting oil in an extruder or by means of extrusion.
[0049] The perforations closed off by the plugs are axial through
tunnels with a perforation volume that is a multiple of a compact
plug volume.
[0050] In order to produce the temperature-independent burning
propellant powder, a solid material is inserted into the openings
and is compacted and secured in the form of plugs that have a
temperature-dependent mobility. The plugs have a higher mobility
(ability to be displaced inside the hole) at a lower deployment
temperature than at a higher deployment temperature, so that the
plugs permit a faster hole burning at a lower deployment
temperature than at a higher temperature.
[0051] The solid material is preferably inserted into the opening
with the aid of a moderator, in particular a moderator that is not
soluble in the grain, and a highly volatile liquid. The complete
process occurs inside a mixing apparatus, e.g. a drum. During the
rotation, the mixture of moderator, liquid and solid material is
pressed successively into the grain holes as a result of the
propellant powder mass pressure or the moist mixture works itself
into the holes under the effect of the propellant powder mass
pressure. It must be noted here that the holes in the propellant
fill up relatively quickly and loosely with the dry solid material.
However, it is important for the effect according to the invention
that a compacted section of solid material is formed at the
entrance to the hole, which can withstand the ignition pressure
wave under the specifically desired conditions. It has turned out
that for the completely treated grain, the solid material density
in the holes decreases from the outside toward the inside, wherein
the relatively loose mass underneath the compacted plug does not
play a critical role in controlling the hole burning.
[0052] The untreated grain, the solid material and the moderator
are processed together with a liquid inside a mixing apparatus, at
a temperature range between 0.degree. C. and 90.degree. C. The
treatment duration ranges from 10 minutes to 3 hours, at a
rotational speed for the mixing apparatus of between 2 and 30
rotations per minute (rpm).
[0053] According to one preferred embodiment, the moderator used
can be radically cross-linked. A radical initiator is additionally
used for cross-linking the solid material.
[0054] The smallest possible amounts of the solid material and the
moderator are used in the mixing apparatus, for example 0.001
weight % to 4 weight %, relative to the weight of the untreated
grain. The solid material and the moderator are typically added to
the mixing apparatus drum in amounts that are noticeably smaller
than 1 weight %.
[0055] The low-viscous liquid is added to the mixing apparatus in
similar amounts: 0.1 weight % to 5 weight %, relative to the weight
of the untreated grain. A low-viscous liquid in this connection is
a liquid that can be moved easily with the dissolved moderator at
room temperature. Low molecular, well-running solvents such as
water, alcohol, toluene, cyclohexane, etc. can be used.
[0056] A radical initiator can be used, for example in amounts of
0.1 mol % to 5 mol % relative to the mol amount of the
cross-linkable moderator, wherein the radical initiator has a high
decomposition stability for the surface treatment temperature
inside the mixing apparatus. The decomposition time during the
surface treatment for half the quantity of the radical initiator,
for example, exceeds 10 hours. At the polymerization temperature,
on the other hand, the radical initiator must decompose quickly
into radicals. In that case, the decomposition time for half the
quantity of the radical initiator can be less than 1 hour.
[0057] After treating the propellant powder with a cross-linkable
moderator and an initiator, atmospheric oxygen must be removed from
the propellant powder by flushing it with inert gas or through a
vacuum/flushing with inert gas at room temperature.
[0058] The cross-linking of the moderator is typically realized
with inert gas under normal pressure, at a temperature of less than
90.degree. C. and during a period of less than six times the
decomposition half-life of the radical initiator at this
temperature.
[0059] Polyvinyl alcohol, poly (.alpha.-methyl styrene), poly(vinyl
alcohol-co-vinyl acetate), poly(vinyl alcohol-co-ethylene),
polybutadienediol, polybutadienediol methacrylate,
polybutadienediol diacrylate or hydrocarbons with even longer
chains, such as waxes, are particularly suitable as moderators that
are not cross-linked. These moderators remain in the plug and on
the propellant surface because they are not soluble in the
propellant powder matrix. No diffusion into the propellant grain or
away from the propellant surface occurs.
[0060] Water, hexane, cyclohexane, toluene or a mixture of
water/ethanol, water/methanol, water/acetone, ethanol/cyclohexane
or toluene/hexane can be used as liquid.
[0061] The following substances can be used, for example, as
cross-linkable moderators: hexanedioldiacrylate,
dipropyleneglycoldiacrylate, ethyleneglycoldimethacrylate,
tetraethyleneglycoldiacrylate, trimethylolpropanetriacrylate,
triethylene glycoldiacrylate, propoxylated glycerin triacrylate,
pentaerythritol tetraacrylate, ethoxylated bisphenol A-diacrylate,
propoxylated neopentylglycol-diacrylate, ethoxylated
neopentyl-glycol-diacrylate, polyethyleneglycoldiacrylate,
polybutadienedioldiacrylate, polybutadienedioldimethacrylate,
polyethyleneglycoldimethacrylate, polypropylene oxide
diacrylate.
[0062] The liquid can be removed by allowing it to evaporate from
the opened mixing apparatus while the mixture is rotated. The
finished propellant is subsequently stored for several days at an
elevated temperature (e.g. 3 days at 60.degree. C.) to remove
residual solvents and other volatile components.
[0063] The perforated propellants can have optional formulations
and dimensions. For example, they can be composed of the following
energy carriers:
[0064] Nitrocellulose with different nitration degrees,
polyglycidylnitrate, poly glycidylazide, polyNIMMO, polyAMMO,
polyBAMO, ethyleneglycoldinitrate, diethyleneglycoldinitrate,
nitroglycerin, butanetrioltrinitrate, metrioltrinitrate,
nitroguanidine, hexogen, octogen, alkyl-NENA, CL-20, DNDA57, NTO,
PETN, etc.
[0065] If necessary, the perforated propellant can contain
additives that are known in propellant production for the
stabilization, barrel protection, plasticizing and gun flash
damping. Known additives for increasing the stabilization are, for
example, Acardit II (CAS No: 724-18-5), Centralit I (CAS No.
90-93-7), Centralit II (CAS No.: 611-92-7), 2-nitrodiphenylamine
(CAS No.: 836-30-6) and diphenylamine (CAS No.: 122-39-4). Talcum
(CAS No.: 14807-96-6), titanium dioxide (CAS No.: 13463-67-7),
calcium carbonate (CAS No. 1317-65-3) or magnesium silicate (CAS
No.: 14807-96-6) can be used for protecting the barrel while
camphor (CAS No.: 76-22-2) or dibutyl phthalate (CAS No.: 84-74-2)
can be used for the plasticizing. Potassium sulfate (CAS No.:
7778-80-5) or potassium cryolite, on the other hand, can be used
for the gun flash damping. The untreated grain can furthermore
contain other additives to improve the ignition behavior and
modulate the burning. All the aforementioned additives can be added
to the powder dough while preparing the untreated grain and are
thus distributed evenly in the grain matrix. The total amount of
additives in the untreated grain is between 0-20 weight %, relative
to the nitrocellulose content, preferably between 0.1-5 weight %.
However, these additives can also be introduced through the surface
treatment according to the invention.
[0066] Additional advantageous embodiments and feature combinations
for the invention follow from the detailed description below and
the complete set of patent claims.
SHORT DESCRIPTION OF THE DRAWINGS
[0067] The following drawings are used to explain the
embodiments:
[0068] FIGS. 1a-c Contrasting of the test results for FM
2032n/9;
[0069] FIGS. 2a-c Representation of the ignited propellant
grains;
[0070] FIGS. 3a-c Pressure bomb tests with untreated grain FM2708n
and with samples for FM2712n and FM2758n;
[0071] FIGS. 4a-b Representation of the pressure curve and the peak
gas pressure in dependence on the temperature during the weapon
firing;
[0072] FIGS. 5a-c Representation of dynamic vivacity of the
untreated, the treated and the aged propellant in the pressure
bomb;
[0073] FIG. 6 Concentration profiles of the cross-linked moderator
(propoxylated glycerin triacrylate) before and after the
accelerated aging (4 weeks, 71.degree. C.);
[0074] FIG. 7 Concentration profiles of the cross-linked moderator
ethylenediglycol dimethacrylate before and after the accelerated
aging (4 weeks at 71.degree. C.);
[0075] FIGS. 8a-c Reduction in the dependence of the burning on the
temperature and ballistic stability for the untreated propellant
that is stored at 21.degree. C. for 4 weeks, and the treated
propellant that is stored at 63.degree. C. for 4 weeks;
[0076] FIGS. 9a-d Pressure bomb firings at different propellant
powder temperatures of the untreated grain (FIG. 9a), the treated
propellant (FIG. 9b), the treated propellant that is aged faster
(FIG. 9c) and a mixture of 70 weight % of untreated grain and 30
weight % of treated grain (FIG. 9d);
[0077] FIGS. 10a-b Pressure bomb firings with propellant that is on
the one hand stored gastight and, on the other hand, artificially
aged.
[0078] FIGS. 11a-b Dynamic vivacity values for the untreated grain
and the treated grain without the addition of plasticizer at
different temperatures inside the pressure bomb.
MEANS FOR REALIZING THE INVENTION
[0079] A special surface treatment is realized to obtain the
temperature-independent propellants according to the invention:
[0080] For this, a solid material, a plug-stabilizing moderator and
a low-viscous liquid are added to the untreated perforated grains
inside a polishing drum and the components are then rotated during
a predetermined time interval, at a specific temperature and with a
specific rotational speed. The individual surface-treatment
materials must be compatible with the untreated grain.
[0081] The compatibility must be determined from case to case with
suitable measuring methods. For example, intensive mixtures of
untreated grain and surface treatment materials must be analyzed in
the heat flow calorimeter (HFC) at 80.degree. C. to determine
extensive heat development, or excessive amounts of the surface
treatment material are deposited on the untreated grain or diffused
into the untreated grain. These samples are then subjected to the
90.degree. C. weight-loss test or are examined in the heat flow
calorimeter (HFC). Another test for determining the compatibility
is the determination of the deflagration temperature of such
surface treatment materials/untreated grain mixtures.
Concerning the Solid Material:
[0082] The solid material used can be a pure material or a mixture
of different solid materials. It is important in this connection
that the average grain size of the solid material or the
solid-material mixture is in a favorable range if the solid
material or the solid material mixture are not soluble in the
low-viscous liquid. It should be possible to insert the solid
material or the solid-material mixture without problems and with
the aid of the mixing apparatus into the hole. The material should
furthermore compact easily, so that the plug is sufficiently firm.
The solid material grain size, for example, should not exceed more
than 1/10 of the hole diameter.
[0083] These grain sizes are between 0.01 and 200 microns,
preferably in the range of 0.1 to 50 microns. (The grain sizes for
the exemplary embodiments, described in the following, ranged from
0.5 to 45 micrometers). The liquid and solid material as well as
the ratio of solid material to liquid should be selected such that
the solid material grains do not agglomerate, but retain their full
mobility. This is important for an efficient capping of the outer
ends of the perforations.
[0084] The average grain size logically does not play a role if the
solid material or the mixture of solid materials is soluble in the
low-viscous liquid.
[0085] Preferred are solid materials or solid material mixtures,
which are not soluble in the liquid used.
[0086] In principle, any type of solid material or solid material
mixture can be used, which is chemically stable in the deployment
temperature range for the propellant powder, is compatible with the
propellant formulation and therefore does not negatively influence
the chemical service life. In addition, the solid material should
not melt over the complete production, firing and storage
temperature range and should not sublimate away and/or diffuse into
the propellant grain to a considerable degree during the complete
service life. The substances are advantageously selected to have a
melting point that is at least 10.degree. C.-20.degree. C. above
the maximum deployment temperature. Preferred are substances with a
melting point above 90.degree. C., which are insoluble in the
propellant formulation or, at best, have only a slight
solubility.
[0087] In addition, solid materials or solid material mixtures that
positively influence the propellant are preferred (low
vulnerability ammunition (LOVA) characteristics, high bulk density,
good pourability, erosion reducing, gun flash damping, high energy
content, electrical conductivity and good ignition ability).
[0088] The solid materials or the mixtures of solid materials
concerned are primarily inert substances.
[0089] Owing to the fact that the propellant powder is ignitable,
the amounts used of the inert solid material or the mixtures
thereof should be as low as possible. Relative to the untreated
grain, between 0.001 and 4 percent inert solid materials or solid
material mixtures are used, preferably between 0.01 and 2
percent.
[0090] Examples of inert solid materials, which can be used in the
pure form or as mixtures, are graphite, talcum, titanium oxide,
potassium cryolite, wolfram trioxide, molybdenum trioxide,
magnesium oxide, boron nitride, potassium sulfate, Acardit,
Centralit, calcium carbonate, oxalamide, ammonium carbamate,
ammonium oxalate, etc. Polymers and copolymers with or without
functional groups, linear, branched or cross-linked are also
considered.
Concerning the Plug Stabilizing Moderator:
[0091] Solid or liquid substances are used as moderators, wherein
the solid moderators should dissolve in the low-viscous liquid,
which is used as third component. Liquid moderators or moderator
solutions can also be present in the low-viscous liquid as
emulsifying agent.
[0092] Suitable as moderators are in principle all solid and liquid
substances, which have a good chemical compatibility with the basic
formulation of the untreated grain and have a low volatility (e.g.
vapor pressure at 21.degree. C. of <10.sup.-2 bar). The
moderator can be used as pure substance or as a mixture of
substances.
[0093] Inert substances are generally used as moderators, but
energetic "moderators" can also be used. However, these must be
insensitive to the mechanical stress exerted during the surface
treatment process, during the later ammunition processing or during
the ammunition transport and deployment.
[0094] The amounts of moderators or moderator mixtures used are
between 0.001 and 4%, preferably between 0.01 and 2%.
[0095] The moderator can either be soluble or insoluble in the
propellant powder matrix. If the moderator is soluble, it is also
referred to as deterrent or deterrent and can be used in accordance
with this function, which is known per se.
[0096] When using a moderator that is soluble in the propellant
powder matrix, a concentration gradient forms in the outer
propellant layer during the surface treatment. This concentration
gradient can break down as a result of diffusion during the service
life of the propellant, which consequently changes the burning
characteristics of the propellant. For the most part, this
manifests itself in higher vivacity and peak gas pressures, which
unfavorably influences the ballistic characteristics. In the
extreme case, it can destroy the weapon.
[0097] This ballistic instability of the propellant (caused by
diffusion processes) must be prevented. The problem of moderator
diffusion therefore is of central importance to the surface
treatment of propellants. The diffusion phenomena depend on the
propellant powder composition, the type of moderator used and the
temperature.
[0098] The diffusion of moderators is favored relatively strongly
if double base or multi-base propellants with high blasting oil
concentrations are used. The surface treatment according to the
invention therefore must be designed in such a way that no change
or only a slight change caused by diffusion of the internal
ballistic characteristics occurs during the propellant storage. If
easily diffused moderators are used, either sufficiently small
amounts must be used, or it must be ensured that the diffusion
process is practically finished before the propellant powder is
packed into the ammunition.
[0099] Alternatively, moderators can be used for the surface
treatment according to the invention, which cannot noticeably
diffuse into the propellant matrix. This can be achieved in two
ways: [0100] 1.) Moderators are used, which are easily dissolved in
the untreated grain matrix and which carry two or more radically
polymerizable groups. Once the moderators are diffused in, they are
polymerized. The resulting network is highly molecular, insoluble
and entangled with the propellant powder matrix and is thus
diffusion stable. [0101] 2.) A moderator is used, which is not
soluble in the untreated grain and additionally has an extremely
low vapor pressure at room temperature. Following the surface
treatment, this moderator only sits on the untreated grain surface
and for affinity reasons can practically not diffuse into the
propellant grain. A moderator loss on the propellant surface as a
result of evaporation/sublimation is negligible with a sufficiently
high molecular weight.
[0102] Low-molecular, soluble moderators, which are suitable for
the surface treatments of double base or multi-base propellant
powders according to the invention, have the lowest possible vapor
pressure at 21.degree. C. and are either liquid materials or solid
materials, if they are soluble in the low-viscous liquid. Suitable
materials include ether, ester, urethane, urea and ketone. Examples
are camphor, dibutyl phthalate, diamyl phthalate, centralit,
dipropyl adipate, di(2-ethylhexyl)adipate, diphenyl urethane,
methyl phenyl urethane, hexanediol-diacrylate,
ethyleneglycol-dimethacrylate, and the like.
[0103] Also suitable are oligomeric, soluble moderators such as
polyether and polyester with molecular weights of 500 to 3000
Dalton. Examples for these are poly(tetrahydrofuran),
polymethylvinylether, poly(oxyethylene), polyethyleneglycol,
poly(butanediol)divinylether, polyester materials such as
SANTICIZER 431, PARAPLEX G-54, or poly[di(ethyleneglycol)adipate,
polyethyleneglycol, polyethylene glycolacrylate,
polyethyleneglycolmethacrylate, polyethyleneglycoldiacrylate, poly
ethyleneglycoldimethacrylate, polyethyleneglycoldimethylether,
poly(propyleneglycol), poly(propyleneglycol)acrylate,
poly(propyleneglycol)diacrylate, poly(propylene glycol)ether,
polycaprolactonediol, polycaprolactonetriol and all co-oligomers
derived thereof. Polymerization reactions are not realized for the
acrylates/methacrylates.
[0104] The radically cross-linkable moderators comprise
low-molecular compounds and oligomers or polymers, which have at
least two groups that can be radically polymerized for each
molecule.
[0105] The radically cross-linked moderators furthermore comprise
mixtures of: [0106] Low-molecular mixtures, respectively oligomeres
or polymers having at least one group that can be polymerized for
each molecule; and [0107] Mixtures carrying at least two groups
that can be polymerized.
[0108] These compounds are either insoluble in the propellant
powder matrix and therefore remain at the propellant surface, or
they are soluble and thus diffuse into the top propellant layer
during the course of the surface treatment according to the
invention. A suitable thermally activated radical starter
(initiator) must then be added to the cross-linkable moderator. The
initiator should easily dissolve in the moderator, such that it is
homogeneously distributed in the moderator. The treatment
conditions and the initiator should be selected such that the
initiator, if possible, cannot decompose into radicals during the
surface treatment process in the polishing drum. If initiator and
polymerized moderator are present either as a layer on the
propellant surface or diffused into the outer propellant layer, the
atmospheric oxygen and, in part, the oxygen present in the outer
propellant layer are removed in the vacuum, at room temperature,
and are replaced with inert gas. This is necessary so that the
radical reactions (polymerization, cross-linking) can occur without
interfering side reactions and result in a high yield. The
propellant temperature is raised high enough under the effect of
inert gas, so that the initiator decomposes as fast as possible and
completely into radicals. These radicals subsequently start the
polymerization or the cross-linking of the moderators.
[0109] Initiators are preferably used as radical starters, which
practically do not decompose into radicals at room temperature, but
decompose very quickly into the respective radicals at temperatures
around 60.degree. C. to 90.degree. C. A quick, careful and complete
conversion of the polymerizable moderators is thus ensured.
Examples for suitable radical starters include tert.
butylperoxyneodecanoat, di(4-tert.butyl
cyclohexyl)peroxydicarbonate, tert. butylperoxypivalate,
diauroylperoxide, bis(azaisobutyronitrile), etc.
[0110] The amount used of the polymerization initiator is based on
the amount of the cross-linkable moderator that is used. Thus,
between 0.1 and 5 mol % initiator, relative to 1 mol moderator are
used. Preferred are initiator amounts between 1 and 4 mol %.
[0111] Moderators that can be cross-linked and are soluble in the
propellant powder are derivatives of diacrylates, triacrylates,
tetraacrylates, dimethacrylates, trimethacrylates,
tetramethacrylates, diacrylamides, triacrylamides,
dimethacrylamides, trimeth-acrylamides, divinylesters,
trivinylesters, divinylethers, trivinylethers, divinyl aromatic
compounds, trivinyl aromatic compounds and the like.
[0112] Examples for low-molecular, radically cross-linkable
moderators are hexanediolacrylate, hexanediolmethacrylate,
ethyleneglycol-dimethacrylate, tetraethylene glycol-diacrylate,
triethyleneglycol-diacrylate, dipropyleneglycol-diacrylate,
trimethylol propane-triacrylate, pentaerythritoltetraacrylate, and
the like.
[0113] Examples for oligomeric, radically cross-linkable moderators
are low-molecular polyethyleneglycoldiacrylate, low-molecular
polyethyleneglycoldimethacrylate, ethoxilated bisphenol
A-diacrylate, propoxylated neopentylglycoldiacrylate, ethoxilated
neopentyl-glycol-diacrylate, propoxylated glycerin-triacrylate,
ethoxilated pentaerythritol-tetraacrylate, and the like.
[0114] Examples for polymeric, radically cross-linkable moderators
are polybutadienediolacrylate, high-molecular
polyethyleneglycoldiacrylate, high-molecular
polyethyleneglycoldimethacrylate, high-molecular
polypropyleneoxidediacrylate, and the like.
[0115] Moderators that dissolve only slightly or not at all in the
propellant powder are solid or liquid compounds, which are soluble
in the low-viscous liquid or at least can be finely emulsified
therein. The compounds in question can be inert or energetic
substances. A precondition is that the moderator concentration on
the propellant surface cannot change through sublimation or
diffusion. This can be achieved by using high-melting low-molecular
or oligomeric or polymeric compounds. In addition, the volatility
of insoluble compounds, containing polymeric groups, following
deposition on the propellant grain can additionally be reduced
through a polymerization reaction (as described in the above).
[0116] Suitable insoluble moderators are apolar polymers and
oligomers or strongly polar polymers and oligomers with or without
polymerizable groups.
[0117] Examples for these include totally or partially hydrolized
polyvinyl acetate, poly(vinylalcohol-co-ethylene), polybutadiene,
polybutadienediol, polybutadiene dioldiacrylate, polystyrene,
polyvinylpyrrolidon, poly(acrylonitrile-co-butadiene),
poly(.alpha.-methylstyrene),
poly(vinyltoluene-co-.alpha.-methylstyrene), and the like.
Concerning the Low-Viscous Liquid:
[0118] The low-viscous liquid necessary to realize the surface
treatments according to the invention is a solvent or solvent
mixture that can easily dissolve or finely emulsify the solid or
liquid, plug-stabilizing moderator and swells the propellant grain
only slightly or not at all. Particularly suitable are liquids with
high or low polarity. The boiling point for the liquid must be
higher than the surface treatment temperature. The low-viscous
liquid nevertheless should have sufficiently high volatility to
permit evaporation at the treatment temperature during a short
period of time (between 5 and 60 minutes). If necessary, the liquid
can also be removed with the aid of a pressure reduction or by
means of a warm gas flow. The liquid can be a pure solvent or a
solvent mixture, wherein amounts of 0.1% to 5% liquid (relative to
the propellant amount), preferably between 0.5% and 2%, are used
for the surface treatment.
[0119] Examples for particularly suitable low-viscous liquids are
water, mixtures of water and methanol, mixtures of water and
ethanol, mixtures of water and propanol, mixtures of water and
acetone, mixtures of water and tetrahydrofuran, as well as pentane,
hexane, heptane, cyclohexane, toluene, methylene chloride and
mixtures thereof.
[0120] Perforated propellants are processed with the
above-mentioned substances inside a polishing drum. For this, the
volume of an optionally large polishing drum of steel or copper is
partially filled with a perforated propellant, wherein the minimum
volume is limited to approximately 10 liters. The desired degree of
filling is between 5 and 50%, preferably between 10 and 40%. The
propellant can be non-graphitized or graphitized. For this, the
solid material or solid material mixture is initially deposited in
the rotating drum and is thus distributed homogeneously over the
complete propellant surface. If the propellant powder used has
already been graphitized sufficiently, it is possible to omit the
further introduction of solid material or a different type of solid
material can be added, if necessary. Following this, a solution
consisting of the low-viscous liquid and the moderator or the
moderator mixture is added. In case of a desired cross-linking of
polymerizable moderators, this solution additionally contains the
polymerization initiator.
[0121] At least one of the solid material components should either
be graphite dust or acetylene carbon black, owing to the fact that
for safety reasons (electrostatic charging during the transport of
propellants), the propellant powder must always be covered with an
electrically conducting material layer.
[0122] If the solid material consists of an inert (non-energetic)
material, it is used only in small amounts (relative to the
propellant). Thus, between 0.01% and 2% solid material is
homogeneously distributed over the propellant powder inside the
polishing drum. If an energetic material is added, a concentration
of more than 2% can be used since this mixture will ignite
better.
[0123] Given an optimum propellant grain flow, the added substances
are allowed to act upon the propellant surface during a specific
time interval and at temperatures of between 0.degree. C. and
90.degree. C., preferably between 20.degree. C. and 70.degree. C.
The reaction process lasts between 5 minutes and 4 hours,
preferably between 15 minutes and 120 minutes. The polishing drum
must be closed gas-tight during the reaction time (depending on the
vapor pressure of the liquid that is used).
[0124] Following the reaction time in a gas-tight treatment
apparatus, the lid on the filling hole is normally removed so that
most of the low-viscous liquid can evaporate. Even this evaporation
process must be exactly controlled with respect to time. The time
interval can be between 5 minutes and 4 hours and is preferably
between 10 minutes and 120 minutes. Additional measures can be used
to aid or support the evaporation, e.g. an air flow or inert gas
flow can be guided over the moist propellant.
[0125] If non-polymerizing moderators are used, the treated
propellant powder is subsequently subjected to a severe drying
process during in which the last traces of solvent are removed and
the treated layer is stabilized. Thus, the propellant powder
typically remains for approximately 3 days inside a forced-air oven
at a temperature of 60.degree. C. Ethanol, for example, can be
removed completely (<0.01%) in this way.
[0126] A corresponding polymerization initiator is furthermore
added if a radically polymerizable moderator is used and a
polymerization reaction must be realized. The surface treatment of
the propellant is realized at the lowest possible temperature and
the low-viscous liquid is removed at the same temperature. The
surface treatment is preferably realized at room temperature.
Subsequently, the propellant powder is freed in the vacuum of
solvent residues and atmospheric oxygen and is subjected to inert
gas. Alternatively, the propellant powder can also be flushed only
with the inert gas to displace the atmospheric oxygen. Argon or
nitrogen, for example, can be used as inert gases. The propellant
powder mass subjected to inert gas is heated only then to the
required polymerization temperature, which normally ranges from
around 30.degree. C. to 60.degree. C. above the treatment
temperature.
[0127] If the treatment is realized at room temperature, for
example, then a polymerization initiator that is thermally stable
at room temperature is used, but which decomposes quickly into the
respective radicals at 50.degree. C. to 80.degree. C.
[0128] The decomposition half-life of a polymerization initiator is
the time, during which half of the initiator had decomposed into
radicals at a specific temperature. This decomposition half-life is
known for all commercially available thermal initiators because of
its central importance. To ensure that the polymerization reactions
are as complete as possible, the duration of the polymerization at
a specific temperature is fixed at four to six times the
decomposition half-life for the initiator used at this temperature.
The propellant powder is then allowed to cool down to room
temperature, either by remaining in the environmental air or being
subjected to inert gas. Owing to the fact that low-boiling, apolar
solvents are preferably used for depositing the polymerizable
moderator, the propellant powder is practically solvent-free
following the evacuation and polymerization steps.
[0129] As a result of the above-presented surface treatment
processes, the entrances to the perforation tunnels are closed off
with compact, condensed plugs, which consist primarily of the solid
materials or material mixtures used and the moderator.
[0130] The low-viscous liquid and/or the moderator (deterrent)
soluble in the propellant powder in this case causes the plug to be
additionally compacted and anchored inside the perforation
tunnel.
[0131] Surprisingly, it was discovered that with a correct
selection of the treatment parameters, all surface-treated,
perforated propellant powders exhibit considerably reduced
temperature dependence or even a mostly temperature-independent
characteristic during the burning. It was observed that with an
ignition at high propellant temperatures, the plugs are anchored
practically permanently inside the perforation tunnels and remain
in place. As a result, the ignition of the propellant during the
first burning phase differs from the classic behavior because of
the changed form function and the inherently fast propellant powder
burning at high temperatures is strongly compensated. If the same
propellant powder is ignited at room temperature, the form function
changes in the sense that a faster surface area enlargement occurs
and thus the gas-formation rate can be adapted to the gas-formation
rate at high deployment temperatures. Finally, it was observed that
for very low propellant temperatures, the gas-formation rate for
perforated propellants adapts to that of an untreated grain as a
result of reaching a classic behavior with respect to form
function.
[0132] The burning inside the propellant perforations is thus
slowed down with increasing propellant temperatures as a result of
the treatment influence on the form function. This counteracts the
rate at which the propellant powder burns, which increases with the
increase in the temperature. In the ideal case, the two effects
balance each other, so that the burning of the surface-treated
propellant is independent of the temperature.
[0133] The active mechanism according to the invention thus differs
completely from other mechanisms described in the literature for
achieving a reduced temperature dependence. In particular, this
mechanism is not based on the (dangerous) embrittlement of the
propellant at low temperatures.
[0134] With the correct selection of the surface treatment
components, this effect is retained even if the treated propellant
is subjected to an accelerated aging process (e.g. stored for 4
weeks at 63.degree. C.) or is stored for a very long time at room
temperature. Thus, the surface-treated propellant has a good
ballistic stability, meaning the ammunition filled with this
propellant can be fired safely and delivers a uniform
performance.
[0135] In addition, it was determined that the surface treatment
according to the invention has a favorable effect on the
pourability and the bulk density of the propellant powder. The bulk
densities of treated propellant powders are therefore up to 10%
higher than the bulk densities of untreated propellant powders.
[0136] Since the casing volume of an existing ammunition component
is predetermined, more propellant powder can be inserted into this
predetermined casing volume with increased bulk density.
[0137] TI (temperature-independent burning characteristic) behavior
and high bulk density make it possible to fill more propellant
powder into existing casings. Thus, the kinetic energy of the
projectile can be raised without exceeding the specified maximum
pressure in the weapon over the complete temperature range for
deployment.
[0138] A propellant that was subjected to a surface treatment
according to the invention is therefore suitable for realizing a
noticeable and cost-effective increase in the fighting efficiency
of presently existing weapon systems, without affecting the
complete system compatibility. This treated propellant furthermore
can also be used in newly developed weapon systems. The ignition,
for example, can be improved and/or the barrel erosion reduced
through an intelligent selection of solid materials.
[0139] The core of the invention can be summarized as follows:
[0140] 1.) A non-volatile solid material is worked into the
perforations of a double base or multi-base propellant grain inside
suitable treatment apparatuses. Used for this are solid materials
with an average grain size that is clearly smaller than the
perforation diameter, suitable moderators for the plug
stabilization and an adequate amount of easily removed low-viscous
liquid. [0141] 2.) The treatment layers formed with the solid
material are compacted and anchored inside the perforations with
the aid of the moderator and the low-viscous liquid, such that with
increasing deployment temperature the closure becomes more
resistant against the ignition shock, thus influencing the form
function. The plug characteristic remains unchanged over the
complete product service life of the propellant (ballistic
stability). [0142] 3.) Type and concentration of the solid
material, the moderator and the low-viscous liquid together with
the surface treatment parameters (mass, temperature, speed,
treatment length, etc) are adapted to each powder grain and the
respective ignition to obtain an optimum result. [0143] 4.) As a
result of a stronger surface treatment (increase in the
concentration of solid material and/or moderator and/or the
treatment duration), the normal temperature dependence of the
propellant combustion can even be inverted. Propellants that are
highly treated in this way burn faster at low temperatures than at
high temperatures ("negative temperature coefficient"). [0144] 5.)
Propellant powders that burn temperature independent can also be
produced by mixing highly treated propellant powder (with inverted
burning) with untreated propellant powder. Generally, the brisance
or shattering power can be varied over a wide range by mixing
treated and untreated propellant powders.
[0145] New types of propellant bulk powders with strongly reduced
to neutral temperature sensitivity (homogeneously treated
propellant powders) can also be produced by controlling the
parameters described in Points 1) to 3).
[0146] The following can be said with respect to the examples
described below: [0147] The propellant powder raw mass consisted of
58% nitrocellulose, 26% nitroglycerin and 16%
diethyleneglycoldinitrate, wherein Acardit II was used as
stabilizer. [0148] The perforated untreated grain was produced in
an extruder with a 19-hole matrix. The matrix dimension is given
for each example. [0149] The treated grain with practically
temperature-independent burning, which was subjected to a surface
treatment, is also referred to as SCDB (surface coated double base)
propellant grain.
EXAMPLE 1 (FM 2032n/9)
[0150] An amount of 90 kilograms of untreated grain, produced with
a matrix of 10.5.times.(19.times.0.2) mm, is placed inside the
treatment apparatus (treatment drum) at a temperature of 16.degree.
C. Added to this are 180 grams graphite (0.2 weight % relative to
the propellant powder) and a solution of 1440 milliliters of 80% by
volume ethanol (16 ml per kilogram propellant powder) and 225 grams
of polytetrahydrofuran 650 (0.25 weight % relative to the
propellant powder).
[0151] In the gastight, sealed drum, the mixture is mixed at
16.degree. C. while rotating at 14 rpm for 30 minutes. Following
this, the lid is removed from the polishing drum and the solvent is
allowed to evaporate during a period of 105 minutes.
[0152] The treated propellant powder is dried at 60.degree. C. over
a period of 3 days.
[0153] FIGS. 1a-c contrast the test results for burning a
propellant powder in the ballistic bomb. The ratio of the momentary
pressure P to the maximum pressure Pmax is plotted on the abscissa
while the dynamic vivacity (1/bar sec).times.100 is plotted on the
ordinate. FIG. 1a shows the behavior of the untreated grain at
deployment temperatures of -40.degree. C., +21.degree. C. and
+50.degree. C. FIG. 1b shows the pressure bomb tests conducted
immediately after the propellant powder production and FIG. 1c
shows these tests conducted after a 5-year storage time at
21.degree. C.
[0154] As compared to the untreated grain, the treated grain
subjected to a surface treatment (SCDB) FM 2032n/9 shows very
little vivacity differences in the 150 ml pressure bomb (charge
density 0.2; firing at -40.degree. C., +21.degree. C. and
+50.degree. C.) for the three propellant powder temperatures. Thus,
the burning for all practical purposes does not depend on the
temperature.
[0155] A portion of the treated propellant powder is stored for 5
years in a closed container at room temperature. A pressure bomb is
again test-fired with this stored propellant powder (FIG. 1c). The
propellant powder shows the same dynamic vivacity values as 5 years
earlier, meaning the burning continues to be
temperature-independent.
EXAMPLE 2 (FM 2712n)
[0156] Placed into a large treatment apparatus are 220 kilograms of
untreated grain, produced with the aid of a
12.0.times.(19.times.0.20) mm matrix, and preheated to 30.degree.
C. Added to this are 187 grams (0.085 weight % relative to the
propellant powder) of graphite and subsequently a solution of 264
grams polytetrahydrofuran 650 (0.12 weight % relative to propellant
powder) and 2040 grams 75% by volume ethanol (10.6 milliliter per
kilogram propellant powder). The mixture is mixed in the closed
drum for 60 minutes at 30.degree. C. and with a rotational speed of
8.25 rpm. Following this, the lid of the polishing drum is removed,
another 187 grams (0.085 weight %) of graphite are added and the
solvent is allowed to evaporate from the rotating drum during a
period of 30 minutes.
[0157] The propellant powder treated in this way is dried over a
period of 3 days at 60.degree. C.
EXAMPLE 3 (FM 2758n)
[0158] This treatment is realized in exactly the same way as for
Example 2.
[0159] To confirm the mechanism of the temperature-independent
burning of the propellant powder, powder grains were tested in a
quenching bomb at different temperatures. A rupture disc opened the
bomb at approximately 700 bar and the burned propellant grains are
thrown into a water bath and quenched. The recuperated, partially
burned propellant grains were then photographed.
[0160] FIGS. 2a-c show the burned propellant grains, which were
fired at -40.degree. C., +21.degree. C. and +50.degree. C. It is
clearly noticeable that at low temperatures, other form function
characteristics contribute to the burning mechanisms than at high
temperatures.
[0161] FIG. 3a, on the other hand, shows the pressure bomb test
results for the untreated grain FM2708n. FIGS. 3b and 3c show the
test results for the two samples FM 2712n and FM2758n. It is quite
obvious that the temperature dependence of the propellant powder
burning could be reduced considerably.
[0162] These samples were also subjected to a weapon firing. FIG.
4b (peak gas pressure in dependence on the temperature) shows that
no great variations in the pressure curve can be detected over the
complete temperature range between -40.degree. C. and +63.degree.
C. The measured muzzle velocities furthermore vary only slightly
(FIG. 4a: muzzle velocity in dependence on the temperature). In
contrast, the untreated propellant powder LKE II is highly
temperature-dependent for the firing.
EXAMPLE 4 (CM 0310n/112)
[0163] An amount of 8 kilograms of untreated grain, produced with a
matrix of 12.0.times.(19.times.0.20) mm, is originally placed into
a treatment apparatus. Added to this are 32 grams (0.40 weight %
relative to the propellant powder) of graphite (grain size 45
microns). The graphite is distributed over the complete bulk powder
surface by rotating the material at 24 rpm for 5 minutes inside the
closed drum.
[0164] Following this, a solution consisting of 100 grams of
cyclohexane (1.25 weight % relative to the propellant powder), 40
grams propoxylated glycerintriacrylate (0.5 weight % relative to
propellant powder) and 2 grams di(4-tert.-butyl
cyclohexyl)peroxydi-carbonate (5 weight % relative to the
triacrylate) are sprayed onto the rotating propellant powder
mass.
[0165] The mass is then rotated for 60 minutes inside a gas-tight,
closed drum at room temperature. Following that, the lid is removed
from the treatment apparatus and the solvent allowed to evaporate
from the rotating drum during a period of 30 minutes.
[0166] The treated propellant powder is transferred to a vacuum
cabinet and is evacuated therein at room temperature until a
terminal pressure of approximately 1 mbar is reached. The vacuum
cabinet is then filled with nitrogen and the heating turned on.
Once the propellant powder has reached a temperature of 70.degree.
C., the propellant powder is exposed for approximately two more
hours to this temperature. The propellant powder is subsequently
allowed to cool down to room temperature.
[0167] HPLC (high-pressure liquid chromatography) testing of the
treated propellant powder showed that the propellant powder no
longer contained free triacrylate.
[0168] The amount of 1 kilogram of the treated propellant powder is
welded into a gas-tight bag and stored for 4 weeks at 71.degree.
C., which corresponds to a storage at room temperature of several
decades (50 to 100 years). The remaining propellant powder is
stored at room temperature.
[0169] Respectively one 150 ml pressure bomb (charge density 0.2)
of the artificially aged sample, of the sample stored under normal
conditions and of the sample with untreated propellant powder is
fired at -40.degree. C., +21.degree. C. and +50.degree. C.
[0170] The results are shown in FIGS. 5a-c. The dynamic vivacity of
the treated propellant powder (FIG. 5b) at the different firing
temperatures no longer differ as strongly as those of the untreated
grain (FIG. 5a). The treated propellant powder has become less
temperature-sensitive. The dynamic vivacity has not changed as a
result of the artificial aging (FIG. 5c) because a diffusion of the
polymerized moderator is no longer possible. On the one hand, this
is due to the strong increase in the molecular weight of the
moderator through cross-linking and, on the other hand, through the
additional entanglement of the polymeric moderator chains with the
nitrocellulose chains. That is to say, the treated propellant
powder has ballistic stability.
[0171] Analyses of the concentration profile by means of FTIR
(Fourier transformation infrared spectrometry) confirm that the
cross-linked moderator no longer can diffuse, as shown in FIG. 6
(relative concentration as function of penetration depth). There,
the concentration gradients for the moderator are unchanged on the
surface of the propellant grains before and after the artificial
aging.
EXAMPLE 5 (FM 2706n/F)
[0172] An untreated grain, produced with the matrix
11.0.times.(19.times.0.20) mm, is treated with a cross-linkable
moderator, in the same way as for Example 4.
[0173] Ethyleneglycoldimethacrylate was used (1.3 weight % relative
to the propellant powder).
[0174] Following the cross-linking of the moderator, the remaining
amount of ethyleneglycoldimethacrylate was determined with the aid
of GC/MS (gas chromatography/microspectrometry). It turned out that
>95% of the dimethacrylate was converted. The propellant powder
was stored at 71.degree. C. for 4 weeks and its concentration
profile was subsequently compared with FTIR microspectroscopy to
the propellant powder stored under normal conditions. The
concentration profiles of the cross-linked moderator, shown in FIG.
7, prove that diffusion cannot be detected even under drastic
storage conditions. In turn, it means that this propellant powder
has ballistic stability.
EXAMPLE 6 (AM 0116n/202)
[0175] An amount of 8 kilograms of untreated grain, produced with a
12.times.(19.times.0.20) mm matrix, is placed into a small rotating
drum. The untreated grain was previously heated to 60.degree.
C.
[0176] Added to the heated, untreated grain rotating at 26 rpm are
12 grams of graphite (0.12 weight % relative to propellant powder).
Once the graphite is distributed homogeneously over the propellant
powder, a solution of 90 grams of water (1.1 weight % relative to
propellant powder) and 5.6 grams of polyvinyl alcohol (0.07 weight
% relative to propellant powder) are added and mixed for 70 minutes
inside a closed drum at 60.degree. C.
[0177] Following this, the lid is removed and the water is allowed
to evaporate from the rotating drum during a period of 20
minutes.
[0178] The treated propellant powder is dried for three days at
60.degree. C.
[0179] FIGS. 8a-c show the pressure-bomb firings at different
propellant powder powder temperatures of the untreated grain (FIG.
8a: untreated), the treated propellant powder (FIG. 8b: following
storage at 21.degree. C. for 4 weeks) and the treated propellant
powder that is aged faster (FIG. 8c: 4 weeks at 63.degree. C.). The
pressure bomb testing clearly shows the reduction in temperature
dependence for the propellant powder burning following the surface
treatment according to the invention. This reduction does not
change if the treated propellant powder is subjected to an
artificial aging process. Polyvinyl alcohol cannot diffuse into the
propellant powder matrix because it is not soluble. The treated
propellant powder is therefore also ballistically stable.
EXAMPLE 7 (AM 0106n/1)
[0180] The amount of 55 kilograms untreated grain, produced with a
rosette matrix of 13.7.times.(19.times.0.26) mm, is placed into a
medium-size surface treatment apparatus that is heated to
30.degree. C. The untreated grain was also preheated to 30.degree.
C.
[0181] Added to the heated, untreated grain rotating at 13.6 rpm
are 55 grams of graphite (0.10 weight % relative to propellant
powder). As soon as the graphite is distributed homogeneously over
the propellant powder, a solution of 512 grams ethanol (75% by
volume ethanol, 25% by volume water), 27.5 grams
polytetrahydrofuran 650 (0.05 weight % relative to the propellant
powder) are added and all ingredients are mixed at 30.degree. C.
for 60 minutes inside the closed drum.
[0182] Following this, the closing lid is removed and the watery
ethanol is allowed to evaporate from the rotating drum over a
period of 15 minutes.
[0183] The treated propellant powder is then dried during a period
of 3 days at 60.degree. C.
[0184] FIGS. 9a-d show the pressure-bomb firings for different
propellant powder temperatures of the untreated grain (FIG. 9a:
untreated), the treated propellant powder (FIG. 9b: following a
storage at 21.degree. C. for 4 weeks) and the treated propellant
powder aged at an accelerated speed (FIG. 9c: for 4 weeks at
63.degree. C.). The pressure bomb testing clearly shows the
reduction in the temperature dependence of the propellant powder
burning following the surface treatment according to the invention.
This reduction does not change if the treated propellant powder is
subjected to an artificial aging process, thus making this
propellant powder ballistically stable as well
[0185] FIG. 9d furthermore shows a mixture of 70 weight % of
untreated grain and 30 weight % of treated grain. The vivacity of
the propellant powder burning can additionally be controlled with
mixtures of this type.
EXAMPLE 8 (AM 0116n/308)
[0186] An amount of 8 kilogram untreated grain, produced with a
matrix of 12.0.times.(19.times.0.20) mm, is placed into a treatment
apparatus at room temperature. Added to this are 16 grams (0.20
weight % relative to propellant powder) of graphite (grain size 45
microns), which is distributed over the complete bulk powder
surface by rotating it in the closed drum for 5 minutes at 24
rpm.
[0187] A solution, consisting of 60 grams cyclohexane (0.75 weight
% relative to propellant powder) and 12 grams
polybutadienedioldimethacrylate (0.15 weight % relative to
propellant powder) are subsequently sprayed onto the graphitized
propellant powder while the propellant powder mass is rotated.
[0188] The mass is mixed at room temperature for 100 minutes inside
the closed, gas-tight drum. Subsequently, the lid of the treatment
apparatus is removed and the solvent allowed to evaporate from the
rotating drum during a period of 20 minutes.
[0189] The treated propellant powder is then dried for 3 days at
60.degree. C.
[0190] A portion of this surface-treated propellant powder is
artificially aged inside a gas-tight bag during a period of 4 weeks
at 71.degree. C. (FIG. 10b), while the remaining portion of the
propellant powder is stored gas-tight at room temperature (FIG.
10a).
[0191] Both propellant powders are fired in the 150 cm.sup.3
pressure bomb at -40.degree. C., +21.degree. C. and +63.degree. C.
The results are shown in FIG. 10. Even though the moderator
deposited on the propellant powder is not cross-linked, a vivacity
change cannot be detected in the pressure bomb before (FIG. 10a)
and after (FIG. 10b) the aging process. It means that the moderator
is not diffused away from or into the propellant powder.
[0192] The analysis of the concentration profiles with FTIR
microspectroscopy, carried out before and after the aging of the
propellant powder, also does not show any changes.
EXAMPLE 9 (17MM2007/TV50)
[0193] With this example, the effect according to the invention is
reached without deterrent.
[0194] A medium-size rotation drum is filled with 55 kg untreated
grain, produced with a matrix of 12.0.times.(19.times.0.20) mm. The
untreated grain was preheated to 30.degree. C.
[0195] Added to the heated, untreated grain inside the drum
rotating at 13.5 rpm are 42 g graphite (0.075 weight % relative to
the propellant powder) and 55 g talcum (0.10%). As soon as the
graphite and the talcum are distributed homogeneously over the
propellant powder, 695 g solvent (ethanol:water, 3:1; 15 ml per kg
of untreated grain) are added and the mixture is then rotated
inside the closed drum for 60 minutes at 30.degree. C.
[0196] Following this, the closing lid is removed and the solvent
allowed to evaporate from the rotating drum during a period of 30
minutes.
[0197] The treated propellant powder is dried for 3 days at
60.degree. C.
[0198] FIG. 11a (untreated grain) and FIG. 11b (following the
treatment according to the invention) show the pressure-bomb
firings at different propellant powder temperatures of the
untreated grain (untreated) and the treated grain (following
storage at 21.degree. C. for 4 weeks). The pressure bomb clearly
shows the reduction in the temperature dependence of the propellant
powder burning following the surface treatment.
[0199] In summary, the following must be noted here: [0200] The
present invention resulted in the new finding that lowering the
temperature coefficient of perforated double-base to multi-base
propellant powders is achieved through a purposeful sealing of the
perforations with plugs, which have a temperature-dependent
mobility. Suitable surface-treatment processes can be used to close
off the holes in the propellant powder, such that the hole burning
is delayed at high propellant powder temperatures, but occurs
immediately at low temperatures (influence on the form function).
This leads to a burning behavior of the surface-treated double-base
propellant powder, which is for the most part independent of the
propellant powder temperature. [0201] Surprisingly, it was found
that with an optimum selection of the treatment components and
parameters and minimum amounts of treatment means, a
temperature-independent burning of the homogeneous, treated
propellant powder can be achieved. The great advantage of this is
that the treated propellant grain can be ignited easily with the
initial ignition. In addition, the surface treatment according to
the invention can be reproduced in such a way that the treated
propellant powder can be used in the pure form (and not necessarily
as a mixture). Thus, a homogeneous combustion can be achieved.
[0202] Surprisingly enough, it was also discovered that the surface
treatment according to the invention permits the production of
ballistically stable propellant powders. A uniform burning is thus
ensured over the complete deployment period for the ammunition
system. [0203] These new types of surface treatments in principle
can be used for any perforated untreated grain, but must be adapted
to the individual formulation and matrix of the propellant powder
as well as the ignition system, so that the temperature dependence
of the propellant powder burning can be optimally adjusted. [0204]
The surface treatment technique that was discovered makes it
possible to produce propellant powders with similarly high
gas-formation rates and thus similar muzzle velocities and peak gas
pressures over a broad temperature range. As a result, a constant
high energy level is available, independent of the environmental
temperature at which the ammunition is fired, and the final
ballistic performance can thus be kept constant and high. [0205]
With the treatment according to the invention, the temperature
behavior of the propellant powder can be varied over a wide
application range, or a desired behavior can specifically be
adjusted. If a weakened form of the surface treatment is realized
(smaller amounts of solid material and/or moderator (deterrent)
and/or shorter treatment times than for the optimum treatment), a
reduced temperature dependence of the propellant powder burning is
achieved. With an optimum treatment, however, the propellant powder
burning is nearly independent of the temperature. If a more intense
surface treatment is realized (larger amounts of solid material
and/or moderator (deterrent) and/or longer treatment times than for
the optimum treatment), the temperature behavior of the propellant
powder can be inverted. In that case, the gas-formation rate of the
treated propellant powder is lower at high temperatures than at low
temperatures. [0206] Thus, a propellant powder with
temperature-independent burning can also be produced when mixing a
highly treated and a non-treated propellant powder at the right
ratio. [0207] The treated bulk powder has improved pourability and
increased bulk density. The bulk density is a measure for the
propellant powder weight that can be inserted into a volume unit
and is typically provided as gram per liter (g/l). This increased
bulk density is of high importance since the casing volume of a
given ammunition component is predetermined. The higher the amount
of propellant powder that can be inserted into a predetermined
casing volume, the more chemical energy is available for the
ballistic deployment. [0208] Since only extremely small amounts of
energetic inert material are used for the new type of surface
treatment, the performance drop of the treated propellant powder
hardly matters (based on the combustion calorimetry, the treated
propellant powder only has approximately 2% less explosion heat as
compared to the untreated grain).
[0209] In particular the excellent deployment service life must be
stressed. Storing the propellant powder over long periods of time
or at high temperatures is possible without essential changes to
the burning characteristic.
[0210] In contrast to prior art, the tendency to brittle fractures
or the development of cross burners during low temperatures is not
favored with the surface treatment according to the invention.
[0211] A temperature-independent burning inside the pressure bomb
or in the weapon can be achieved by using the smallest possible
amounts of treatment means, without this worsening the ignition
behavior.
[0212] The treatment process is simple, reproducible and relatively
cheap.
* * * * *