COMBUSTIBLE PROPELLANT CHARGE SLEEVE

Description

BACKGROUND OF THE INVENTION

The present invention relates to a combustible propellant charge sleeve with MoO₃ and/or WO₃ particles, a method for manufacturing the combustible propellant charge sleeve and a use of the combustible propellant charge sleeve for firing ammunition.

When firing ammunition from an armor barrel, the burning of the propellant powder results in high temperatures and pressures, which lead to severe wear of the armor barrels, especially with large-caliber projectiles such as those used for artillery guns and tanks.

To reduce wear, erosion-reducing additives can be added to the propellant powder or the combustible propellant charge sleeve enclosing the propellant powder, for example wax or kerosene, as described in DE 39 27 400 A1.

EP 1 227 295 A1 describes that erosion-reducing additives can be added to a propellant charge sleeve in the form of oxides of rare earth elements or one of the elements of the sixth subgroup of the periodic table or polyoxymethylene.

EP 1 647 538 A1 describes the addition of polyacetylene or a mixture of WO₃ or MoO₃ and CeO₂ or La₂O₃ or Y₂O₃ in the form of particles to a propellant charge sleeve to reduce erosion, wherein the average particle size is 1 to 10 μm and the maximum particle size is 30 μm.

Tungsten trioxide (WO₃) and molybdenum trioxide (MoO₃) can be used as an additive in the propellant charge sleeve to reduce barrel erosion and thus barrel wear to a certain extent, presumably by trapping atomic hydrogen. However, the barrel wear of this ammunition still needs to be improved in order to reduce the maintenance effort, increase the service life of the armor barrel and, in particular, improve the precision when firing the ammunition, as an eroded barrel shows a significantly reduced firing accuracy.

SUMMARY

An embodiment as shown and described herein may include a combustible propellant charge sleeve for ammunition which can be fired from an armor barrel including a pulp, nitrocelluslose, 5-10% by weight of MO₃ particles, based on the total weight of the propellant charge sleeve, wherein M=Mo and/or W, and 0.01-2% by weight of cationic surfactant, based on the total weight of the propellant charge sleeve, wherein the average particle size d₅₀ of the MO₃ particles is 0.5-2.0 μm, the maximum particle size d₁₀₀ of the MO₃ particles is ≤20 μm, and the quotient of the average MO₃ concentration in % by weight in a volume element of about 0.05 to 1.0 cm³ (C_VE) at any point in the propellant charge sleeve and the total MO₃ concentration in % by weight (C_total) in the propellant charge sleeve is C_VE:C_total=0.80-1.20.

It is therefore a object of the invention to reduce barrel wear in ammunition that can be fired from an armor barrel, particularly in artillery or tank barrels.

This object is solved by a combustible propellant charge sleeve, a method for manufacturing a combustible propellant charge sleeve and a use of a combustible propellant charge sleeve.

DETAILED DESCRIPTION

One aspect of the invention relates to a combustible propellant charge sleeve for ammunition which can be fired from an armor barrel, comprising: pulp, nitrocellulose, 5-10% by weight of MO₃ particles, based on the total weight of the propellant charge sleeve, wherein M=Mo and/or W, and 0.01-2% by weight of cationic surfactant, based on the total weight of the propellant charge sleeve, wherein the average particle size d₅₀ of the MO₃ particles is 0.5-2.0 μm, the maximum particle size d₁₀₀ of the MO₃ particles is ≤20 μm, and the quotient of the average MO₃ concentration in % by weight in a volume element of about 0.05 to 1.0 cm³ (C_VE) at any point in the propellant charge sleeve and the total MO₃ concentration in % by weight (C_total) in the propellant charge sleeve is C_VE:C_total=0.80-1.20.

A further aspect of the invention relates to a method of manufacturing a combustible propellant charge sleeve, comprising the steps of: (a) preparing a slurry of the pulp, the nitrocellulose, and the MO₃ particles, wherein M=Mo and/or W, and cationic surfactant in water, (b) mixing the slurry, (c) dewatering the slurry on a sieve mold to prepare a raw felt, (d) pressing the raw felt and (e) drying to form a combustible propellant charge sleeve.

According to the invention, MO₃ particles are understood to be MoO₃ particles (molybdenum trioxide particles) or WO₃ particles (tungsten trioxide particles). Preferred are WO₃ particles.

In the context of the invention, it was found that propellant charge sleeves of the prior art with metal oxide particles such as MoO₃ or WO₃ particles exhibit strong fluctuations in the concentration of the metal oxides in the propellant charge sleeve and that this is at least one factor for the still too high barrel wear after firing ammunition with corresponding propellant charge sleeves.

Surprisingly, the use of a cationic surfactant in the manufacturing process leads to a relatively uniform and small particle size of the MoO₃ and/or WO₃ particles and to a lower concentration variation of the MoO₃ and/or WO₃ in the combustible propellant charge sleeve, thus avoiding temperature and pressure peaks during firing and thereby reducing barrel wear.

Without being bound to it according to the invention, it is assumed that the cationic surfactant, in conjunction with a relatively small particle size and narrow particle size distribution, counteracts sedimentation of the MoO₃ and WO₃ particles in the manufacturing process, which on the one hand promotes effective recrystallization of the MoO₃ and WO₃ in the pulp (slurry) and thus enables a relatively uniform particle size distribution. On the other hand, the dispersion effect of the surfactant, i.e. the in-suspension holding of the MoO₃ and/or WO₃ particles, promotes an attachment of the particles to the fibers of the nitrocellulose and the pulp (cullulose), which prevents the MoO₃ and/or WO₃ particles from sinking as a result of gravity. This leads to a lower fluctuation in the concentration of the MoO₃ and/or WO₃ particles in the finished propellant charge sleeve. This is particularly relevant for the MoO₃ and WO₃ particles used according to the invention, as the density of these substances is particularly high.

The particle size and particle size distribution are determined using laser diffraction in a wet measurement (Malvern system, Mastersizer E, wet measurement in water in a cuvette). It provides a distribution curve of the particle sizes. d_x means that x volume percent of the particles have a diameter that is smaller than the specified value. For example, with a d₅₀ value (average particle size) of 1 μm, 50% by volume of the particles have a diameter ≤1 μm (micrometers). With a d₁₀₀ value (maximum particle size) of 10 μm, 100% by volume—of the particles have a diameter ≤10 μm.

For the purposes of the invention, a surfactant is understood to be a substance that is surface-active and thus reduces the surface tension of a liquid or the interfacial tension between two phases, thereby supporting the formation of dispersions such as suspensions. Cationic surfactants have positively charged groups such as quaternary ammonium groups.

For the purposes of the invention, polyamines are understood to be saturated, open-chain and/or cyclic organic compounds with terminal amino groups and optionally secondary and tertiary amino groups. Such a polyamine can be prepared, for example, by reacting ethylenediamine and/or propylenediamine with ethylene oxide with complete or almost complete substitution of the oxygen atoms. It is also possible, for example, to react ethylenediamine and/or propylenediamine with epichlorohydrin with complete or almost complete substitution of the oxygen and chlorine atoms. Such polyamines can be present in oligomeric or polymeric form. A cationic surfactant derived from a polyamine is, for example, the salt of a polyamine with an acid, such as acetic acid.

In a preferred embodiment of the invention, the cationic surfactant has two or more cationic groups. Preferably, the cationic surfactant is a salt of an organic polyamine and/or polyethylenimine with an acid. The acid can be an organic or inorganic acid, preferably an inorganic acid, for example hydrochloric acid or sulfuric acid. Further preferred is a surfactant which is available under the trade name Paragas. Paragas is a mixture of various compounds, essentially the salt of a polyethylene amine/imine with an acid. With these preferred cationic surfactants, particularly constant MO₃ concentrations can be achieved in the propellant charge sleeve, i.e. low variations in concentration, which means that particularly low barrel wear can be achieved during firing.

The combustible propellant charge sleeve according to the invention contains 0.01-2% by weight of cationic surfactant, preferably 0.05-1% by weight, more preferably 0.07-0.8% by weight, even more preferably 0.1-0.6% by weight, particularly preferably 0.3-0.5% by weight of cationic surfactant. With these concentrations, very constant MO₃ concentrations can be achieved in the propellant charge sleeve according to the invention and thus a particularly low barrel wear during firing.

The combustible propellant charge sleeve according to the invention is characterized by the fact that the concentration of MoO₃ and/or WO₃ particles in the propellant charge sleeve is more constant than in propellant charge sleeves of the prior art, in which the concentration within the propellant charge sleeve fluctuates strongly and is also subject to strong fluctuations from sleeve to sleeve. A difference in concentration around an average value of, for example, 8% by weight of—3% by weight within known propellant charge sleeves, i.e. a minimum value of 5% by weight, is common. In contrast, the concentration fluctuations of the MoO₃ and/or WO₃ particles in the propellant charge sleeve according to the invention are lower, preferably ≤1.5% by weight, more preferably ≤1.0% by weight, particularly preferably ≤0.7% by weight, especially ≤0.5% by weight. In the axial direction of the propellant charge sleeve, the concentration fluctuations are preferably even lower, preferably ≤1.0% by weight, more preferably ≤0.5% by weight.

The MoO₃ and WO₃ concentration is measured using wet chemistry by cutting out a piece of the propellant charge sleeve, e.g. punching out, e.g. 1 cm×1 cm×wall thickness of the propellant charge sleeve (usually 3.3 mm), and destroying it by fuming with conc. nitric acid and then incinerating it in a muffle furnace at 800° C. The ash content of the preliminary sample (slurry of nitrocellulose and pulp (cellulose) without WO₃) and the loss on ignition of the tungsten trioxide are taken into account. By determining the residual moisture in the sample, the analytical result can be stated in terms of dry matter.

w ⁡ ( Talk , W ⁢ 0 3 ) = m W ⁢ e ⁢ i ⁢ g ⁢ h - Out · 10 6 m W ⁢ e ⁢ i ⁢ g ⁢ h - I ⁢ n · ( 100 - w ⁡ ( H 2 ⁢ O ) ) · ( 100 - G ⁢ V ) - w ⁡ ( ash )

• • m_Weigh-Out=mass of the pellet used after annealing [g]
  • m_Weigh-In=mass of the pellet used before annealing [g]
  • w(H₂O)=water content of the pellet used [%]
  • GV=loss on ignition of the talc or tungsten trioxide [%]
  • w(ash)=ash content of the preliminary sample, calculated on dry matter [%]

To determine the total MoO₃ and/or WO₃ concentration, a wet chemical measurement is carried out on the entire propellant charge sleeve using the above method. Alternatively, at least three wet-chemical measurements of approximately 0.05 to 1.0 cm³ volume each can be carried out at randomly selected points of the propellant charge sleeve according to the above method and the arithmetic mean value can be formed therefrom. The total MoO₃ and/or WO₃ concentration (C_total) in the propellant charge sleeve is the total mass of MoO₃ and/or WO₃ in the propellant charge sleeve divided by the total mass of the propellant charge sleeve.

The quotient of the average MO₃ concentration in % by weight in a volume element of about 0.05 to 1.0 cm³ (C_VE) at any point in the propellant charge sleeve and the total MO₃ concentration in % by weight (C_total) in the propellant charge sleeve is C_VE:C_total=0.80-1.20, preferably 0.85-1.15, most preferably 0.90-1.10, where M=Mo and/or W, preferably W.

The volume element of 0.05 to 1.0 cm³ preferably has a volume of about 0.1 to 0.8 cm³, more preferably about 0.2 to 0.6 cm³, in particular about 0.33 cm³. Further preferably, it is a continuous volume element. In a preferred embodiment of the invention, the volume element has the wall thickness of the propellant charge sleeve. A propellant charge sleeve usually has a length of about 30-90 cm (centimeters), a diameter of 100-160 mm (millimeters) and a wall thickness of about 2-4 mm, in particular 3.3 mm.

Preferably, the volume element for determining C_VE has a size of 0.5 cm×0.5 cm×0.2 cm to 1.5 cm'1.5 cm×0.4 cm, preferably 0.5 cm×0.5 cm×0.33 cm to 1.5 cm×1.5 cm×0.33 cm, particularly preferably 1.0 cm×1.0 cm×0.33 cm. These volume elements, which have the wall thickness of the propellant charge sleeve as their thickness, thus reflect the deviations in the axial direction of the propellant charge sleeve in several measurements. The deviation from the mean value is particularly small in the axial direction. For a volume element for the determination of C_VE with a size of 0.5 cm×0.5 cm×0.2 cm to 1.5 cm×1.5 cm×0.4 cm, C_VE:C_total is preferably 0.85-1.15, preferably 0.90-1.10, particularly preferably 0.92-1.08. This reflects the concentration variation in the axial direction.

In a preferred embodiment of the propellant charge sleeve according to the invention, the average particle size d₅₀ of the MO₃ particles is thus 0.5-2.0 μm, the maximum particle size d₁₀₀ of the MO₃ particles is ≤20 μm, and the quotient of the average MO₃ concentration in % by weight in a volume element (C_VE) at any point in the propellant charge sleeve and the total MO₃ concentration in % by weight (C_total) in the propellant charge sleeve is C_VE:C_total=0.85-1.15, preferably 0.90-1.10, particularly preferably 0.92-1.08, wherein the volume element has a size of 0.5 cm×0.5 cm×0.2 cm to 1.5 cm×1.5 cm×0.4 cm, wherein the propellant charge sleeve has a wall thickness and the 0.2 cm to 0.4 cm is the wall thickness of the propellant charge sleeve.

As an alternative to the wet chemical determination described above, the MoO₃ and/or WO₃ concentration can be measured using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). For this purpose, a section of the propellant charge sleeve is prepared and an SEM-EDX measurement is carried out on an area of approximately 100 μm×100 μm. The measurement is a surface measurement and shows the MO₃ and/or WO₃ concentration in the upper layer of the section. It is given in percent by weight. Preferred is the wet chemical determination as described above.

In a preferred embodiment of the invention, the MoO₃ and/or WO₃ particles have a relatively uniform particle size, i.e. the particle size distribution is comparatively narrow. This is reflected by a low d₁₀₀ value compared to the dso value. According to the invention, the d₅₀ value of the MO₃ particles (MoO₃ and/or WO₃ particles) is 0.5-2.0 μm, preferably 0.7-1.6 μm, particularly preferably 0.8-1.4 μm and most preferably 0.9-1.1 μm. The d₁₀₀-value of the MoO₃ particles and/or WO₃ particles is ≤20 μm, preferably ≤15 μm, more preferably ≤12 μm, particularly preferably ≤10 μm. With these particle sizes, on the one hand very constant MO₃ particle concentrations can be achieved in the propellant charge sleeve according to the invention, i.e. particularly low concentration variations, as a result of which low barrel wear can be achieved during firing, and in addition these uniform particle sizes have the advantage that they themselves ensure low temperature and pressure peaks during firing, as a result of which barrel wear can be reduced even further.

A uniform particle size in the sense of a narrow particle size distribution is achieved by mixing the slurry in the process according to the invention in the presence of a cationic surfactant, preferably for at least 15 minutes. Mixing is preferably carried out by stirring. Without being bound to it according to the invention, it is assumed that the cationic surfactant is placed around the regularly slightly negatively charged MoO₃ and/or WO₃ particles (MoO₃ and WO₃ are slightly acidic in the aqueous environment), whereby the MoO₃ and/or WO₃ particles are kept in suspension, thereby promoting recrystallization, i.e. dissolution and recrystallization. Even if a broad particle size distribution of the MoO₃ and/or WO₃ particles is used, the particle size distribution in the propellant charge sleeve is very narrow, for example d₅₀=0.5 to 2.0 μm, preferably 0.8 to 1.4 μm, with d₁₀₀≤15 μm, preferably ≤12 μm, particularly preferably ≤10 μm, after the process according to the invention has been carried out. The particle size distribution is narrowed and this ensures a more uniform thermal load and pressure load in the armor barrel, which avoids thermal peaks and pressure peaks and reduces barrel wear.

The average concentration of MO₃ in the propellant charge sleeve (total MO₃ concentration) according to the invention is 5-10% by weight, preferably 6-9% by weight, particularly preferably 7-8% by weight, with M=Mo and/or W. M is preferably tungsten (W). In a preferred embodiment of the invention, the propellant charge sleeve contains, in addition to the MoO₃ and/or WO₃ particles, less than 1% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.1% by weight of other metal oxide particles.

The combustible propellant charge sleeve according to the invention preferably contains 45-65% by weight, in particular 52-58% by weight, of nitrocellulose and/or 25-50% by weight, in particular 33-40% by weight, of pulp.

The method according to the invention comprises the steps of: (b) manufacturing of a slurry of pulp, nitrocellulose, MO₃ particles, wherein M=Mo and/or W, and cationic surfactant in water, (b) mixing the slurry, preferably for at least 5 minutes, more preferably at least 20 minutes, particularly preferably 30 minutes to 2 hours, (c) dewatering the slurry on a sieve mold to prepare a raw felt, (d) pressing the raw felt and (e) drying to form a combustible propellant charge sleeve.

In a preferred embodiment of the invention, the slurry in step (a) contains 5-10% by weight of MO₃ particles, based on the total weight of pulp, nitrocellulose, MO₃ particles and cationic surfactant and/or 0.1-2% by weight of cationic surfactant, based on the total weight of pulp, nitrocellulose, MO₃ particles and cationic surfactant.

The method according to the invention preferably comprises the steps of (c) manufacturing of a slurry from pulp, nitrocellulose, 5-10% by weight of MO₃ particles, based on the total weight of the propellant charge sleeve, wherein M=Mo and/or W, and 0.1-2% by weight of cationic surfactant, based on the total weight of the propellant charge sleeve, in water, (b) mixing the slurry, preferably for at least 5 minutes, more preferably at least 20 minutes, particularly preferably 30 minutes to 2 hours, (c) dewatering the slurry on a sieve mold to prepare a raw felt, (d) pressing the raw felt and (e) drying to form a combustible propellant charge sleeve.

The surfactant preferably accumulates partially on fibers, so that the amount of surfactant in the sleeve is preferably somewhat less than in the slurry used.

In a preferred embodiment of the method according to the invention, in step (a) 45-65% by weight nitrocellulose, 25-50% by weight pulp, 5-10% by weight MoO₃ particles and/or WO₃ particles, (d)—2% by weight of cationic surfactant, the % by weight in each case based on the total mass of nitrocellulose, pulp, MoO₃ particles and/or WO₃ particles and/or cationic surfactant, and optionally additives, stabilizers and/or binder resin, a slurry is prepared in water. It is understood that the sum of the weight percentages of the individual components is 100% by weight. A preferred stabilizer is acardite.

The pressing of the raw felt in step (d) is preferably carried out at 20-175° C., more preferably 100-175° C., most preferably 120-150° C.

The drying is preferably carried out under ambient conditions, in particular in a so-called standard climate conditions.

In a preferred embodiment of the process according to the invention, a stabilizer is additionally added in step (a). The stabilizer is preferably acardite (diphenylamine). This stabilizer serves in particular to stabilize the nitrocellulose.

In a further preferred embodiment of the method according to the invention, a binding resin is additionally added in step (a). The binding resin can be added, for example, in the form of binding resin particles. During subsequent pressing at elevated temperature, the binding resin melts and bonds the fibers together. The binding resin is preferably a polymer or a polymer mixture of polystyrene-polybutadiene rubber (latex).

In a preferred embodiment of the invention, a lacquer is applied to the surface of the propellant charge sleeve after step (e). A nitrocellulose lacquer is preferred. Preferably, when a lacquer is used, the binding resin described above is added in step (a).

In a further preferred embodiment of the method according to the invention, a plastic is applied to the surface of the pressed raw felt between steps (d) and (e). The plastic is preferably a polyurethane (PU). This is preferably carried out by immersing the pressed raw felt in a bath of polyols with isocyanate crosslinker and then drying, wherein the polyurethane hardens.

Preferably, the method according to the invention comprises the steps of: (e) manufacturing of a slurry from pulp, nitrocellulose, MO₃ particles, wherein M=Mo and/or W, and cationic surfactant in water, (b) mixing the slurry, preferably for at least 15 minutes, (c) dewatering the slurry on a sieve mold to prepare a raw felt, (d1) pressing the raw felt, (d2) applying of a plastic, preferably a polyurethane, to the surface of the pressed raw felt and (e) drying to form a combustible propellant charge sleeve.

The method according to the invention also preferably comprises the steps of: (f) manufacturing of a slurry from pulp, nitrocellulose and binder resin particles in water, addition of MO₃ particles, wherein M=Mo and/or W, and cationic surfactant in water, (g) mixing the slurry, preferably for at least 15 minutes, (h) dewatering the slurry on a sieve mold to prepare a raw felt, (i) pressing the raw felt and (j) drying to form a combustible propellant charge sleeve, (k) applying of a lacquer to the surface of the combustible propellant charge sleeve, preferably a nitrocellulose lacquer.

Mixing of the slurry is preferably carried out using conventional stirring tools, such as rotating knives. The slurry is dewatered by pouring the slurry onto a sieve mold and allowing the water to flow out through the holes in the sieve, possibly supported by a vacuum. The raw felt is then pressed onto this sieve mold with a suitable counterpart to produce a still slightly moist propellant charge sleeve, which is then dried to produce the combustible propellant charge sleeve according to the invention.

The present invention also relates to the use of the propellant charge sleeve according to the invention for firing ammunition, in particular artillery ammunition.

The invention is explained further below with reference to two examples:

EXAMPLE 1

Preparation of Combustible Sleeves for Tank Gun Ammunition

Pulp sheets are beaten in water (2627 liters of process water) to form a fiber mash. This takes place in a container with a rotating knife at the bottom. Weigh-in weight 78.8 kg. The fiber mash is then ground in a refiner. A further 1200 liters of process water are added.

Nitrocellulose is stirred into the fiber mash. Weigh-in 120.0 kg.

Control of stock density approx. 8%

Addition of a further 1600 liters of process water.

Addition of Paragas: The Paragas is mixed with water and added to the batch while stirring.

The stabilizer Akardit is added: The Akardite is slurried in water and ground. It is then added to the batch while stirring.

16.8 kg of WO₃ particles are slurried in 32 liters of water and added to the batch while stirring.

The batch is pumped into the target container and diluted with process water.

The fibers are separated in special basins, which are in exchange with the target container, on sieve forms by suction. This produces the raw felt.

The raw felts are then pressed at approx. 170° C. During pressing, the water in the raw felt is removed by vacuum. In this step, the sleeve is produced in its defined shape.

The pressed sleeves are PU-impregnated by briefly immersing them in a bath of polyols with isocyanate crosslinker and then drying and curing them in a drying tunnel.

Conditioning in a standard climate (drying).

Mechanical cutting to length and chamfering.

EXAMPLE 2

Preparation of Combustible Sleeves for Artillery Ammunition

Steps 1-3 are identical.

Step 4 here is the addition of binding resin particles. These binding resin particles are later melted during pressing and bond the fibers together. These are polymers made from polystyrene-polybutadiene-latex.

Raw felt production and pressing analogous to the above process.

Step 11 is omitted here.

Steps 12 and 13 are carried out in the same way.

This is followed by a lacquer step. The lacquer is applied using an NC paint with the appropriate color pigment.

It is understood that the features mentioned above and those to be explained below can be used not only in the combinations indicated, but also in other combinations or in a stand-alone position, without going beyond the scope of the present invention. The aforementioned advantages of features or of combinations of several features are merely exemplary and can take effect alternatively or cumulatively. The combination of features of different embodiments of the invention or of features of different claims is possible in deviation from the selected references of the claims.