FR2536065A1 - Propellants based on plastics foam - Google Patents

Abstract

Compsns. for munitions of all calibres and for pyrotechnic lauchers comprise (a) 15-25 wt.% of a plastics (e.g. polyurethane) foam with a density of 0.5-1.2 g/cc, (b) 40-80 wt.% of NH4NO4 granules with a particle size of 0.8-2 mm, and (c) 5-35 wt.% of one or more secondary explosives, esp. nitramine. The nitramine is pref. in the form of granules with a surface area of 6-12 square cm/g, opt. coated with 0.3-1 wt.% of polyurethane, ethyl cellulose, a lacquer, a polyester, graphite, wax or aerosil. The compsns. comprise inexpensive components which can be obtd. in reproducible quality. They have higher energy content than compsns. comprising only polyurethane and nitramine (cf. DE2809279)

Description

 Propulsive charge for a tube weapon.

The invention relates to propellant compositions containing foam and intended to be used for ammunition of all calibres as well as for pyrotechnic ejection means, these fillers containing a plastic foam with a density of 0.5 1.2 g / cm3 with one or more secondary explosive materials
According to the German Patent 28 09 279 propellant charge compositions which consist mainly of 10 to 25% of plastic foam with 90 to 75 g of secondary explosive material such as hexogen and / or octogen The density of these propellant charges is 0.4 to 1.0 g / = m3
The secondary explosives have a uniform particle size fraction, in which the grain size ranges from 0.5 to 2.0 mm.

The size of the grains is adjusted according to the caliber of the ammunition, so that it increases for the big caliber This relation between the caliber and the size of the grains is due to the need to keep within a definable size the surface of the active substance fired, this magnitude being that which is necessary for the acceleration of the projectile in the tube.

It must also be prevented that the firing, once initiated, turns into explosion or detonation. Good firing results have been obtained with the propulsive charges described (in this prior patent)
However, the high proportion of secondary explosives is relatively very expensive, and the manufacture of large grains is difficult Another disadvantage is the relatively low mechanical resistance of these grains to impacts, especially when the grains do not have a monocrystalline structure but consist of crystals having crystallized together.

 Because of these disadvantages, the use of the propellant charge compositions described above is limited to small and medium gauges.

 The invention aims to achieve, under good economic conditions, propellant charge compositions of good efficiency and having a stable combustion, suitable for all weapons calibres and all pyrotechnic ejection devices.

 This result is achieved, according to the invention, with a composition of the kind stated at the beginning, containing a plastic foam with a density of 0.5 to 1.2 g / cm3 with one or more secondary explosive materials, characterized in that the proportion by weight of plastic foam such as polyurethane foam is from 15 to 25%, the proportion by weight of the secondary explosives being from 5 to 35%, while said composition also contains, in a proportion by weight of 40 to 80% Ammonium nitrate granules of different sizes adapted to the size and method of use, with a granulometry of 0.8 to 2 mm.

Other embodiments of the invention are characterized by the following provisions: a) the surface area of the nitramine fraction is 6 to 12 cm 2 / g; b) secondary explosive is coated with an adherent layer
compact and free of bubbles, made of plastic or
inert material, in a weight ratio of 0.3 to 1 5,
relative to the weight of secondary explosive; (c) the nitramine moiety consists of one or more
defined size fractions; d) for a relatively strong propellant charge with a density
of 0.8 g / cm 3, the nitramine fraction is 35 g by weight,
with a particle size close to 0.8 mm the nitrate fraction
ammonia is 45% by weight, and the foam fraction is
20% by weight; e) for a relatively slow charge with a density of 0.8
g / cm3, the nitramine fraction is 10% with a granulo
metric close to 0.4 mm, the ammonium nitrate fraction is
67 by weight and the foam fraction is 20% by weight; f) the coating layer of the secondary explosive grains is
made of polyurethane, ethylcellulose, lacquer or poly
ester, and, as regards the inert material, graphite,
wax or aerosol.

 Quantitative compositions are determined to a large extent by the surface state of the substance having the best reactivity and the best reaction rate.

In practice, this means that it will now be possible to use granulometric fractions of nitramine which are common in the explosives technique (particle size fractions from 0.1 to 1.0 mm), and which are easy to manufacture. The lower sensitivity to the effects of rupture in case of shock is an additional advantage.

 The use of finely ground ammonium nitrate with a particle size of 5 to 50 μm is already known, as well as the manufacture of propellant charges of artillery nitrocellulose or ntrocellulose-nitroglycerine, and same as the manufacture of propellant charges of rockets based on plastic (composite).

According to the invention, on the other hand, granulated ammonium nitrate of common commercial type, having a particle size of 0.8 to 2 mm, is used, and in addition this nitrate is coated with a porous plastic mass with a density of 0.5 to 1.2 g / cm3. In the case of propellant charges already known and described above, it is necessary to provide a compact and non-porous coating mass,
3 with a density of 1.4 to 1.6 g / cm, without which there would be a combustion whose speed could not be controlled. Thanks to the exclusive use, according to the invention, of large granules, it becomes possible to keep the nitramine content very low, without loss of energy, and to obtain the usual burn rate and necessary for the material of artillery, at pressures between 2500 and 5000 bars. In addition to granules of pure ammonium nitrate, it is also possible to use granules containing, inter alia, potassium nitrate as an additive to modify the point of transformation. This makes it possible to dispense with having to add other constituents intended to attenuate the initial energy.

 The thin coating layer on the nitramine considerably increases the mechanical strength of the active substance and provides a homogeneous distribution of this substance within the propellant composition, thanks to the smooth surface of the grains.

 The thickness of the coating layer is calculated so that it has the least possible retardation effect. This layer covers the irregularities of the single crystal, such as vertices; furrows, striations, flats or fracture surfaces. There are no longer any different surfaces for the same uniform particle size. This provides a stabilizing effect of the combustion properties. A minimum gap between the uncoated explosive grains is achieved with uniform distribution of the ammonium nitrate granules. In the case of formation of lumps, the coating layer opposes an increase in the reaction rate, thus undoubtedly avoiding a too sudden and too high rise in pressure.

 The coating layer also prevents the formation of explosive dust, so that reactive surfaces of different sizes are not formed.

 In addition, this layer provides greater resistance of single crystals to impacts, which certainly prevents any breakage of these crystals. During the combustion of the propellant charge, the rise in pressure of the released gases has no influence on the configuration of the single crystals. No new uncontrolled surfaces are thus formed, which can give rise to peaks of rise in pressure.

 The propellant charge compositions according to the invention are very advantageous from an economic point of view, since all their constituents are available on the national market in an exactly defined state, which makes it possible to introduce these compositions into the low-pressure socket. temperature, since they are directly mixable and directly obtained in the form of a foam. In addition, they are exactly reproducible with respect to their performance parameters, such as energy content per unit volume.

These compositions can also be used without a sleeve, in the form of gargousses.

To optimize the propellant charges according to the invention with regard to the desired rate of combustion and / or the quickness of action, the following parameters are available, in the context of the composition indicated above.
Chemical parameters
Nitramine reactive constituent content
Ammonium nitrate oxidizing agent content
Addition of other gas-releasing substances, such as
that nitroguanidine
Physical parameters
Granulometry of nitramine
Density of the propellant composition (porosity)
Density of loading in the combustion chamber
Solidity of grains (grain shape)
Surface coatings.

The following factors influence the rate of combustion:
Surface / volume ratio of the nitramine and ammonium nitrate constituting the oxidizing agent
Proportion of polyurethane foam (retarding effect) 0
It is possible to combine the effects of the retarding agent with those of the critical diameter of the explosive (formation of lumps) in such a way that no excessive reaction or sudden rise in pressure occurs.

Compared to the current state of the art, the propellant compositions according to the invention have better safety characteristics, thanks to their lower secondary explosive content content. Nevertheless, they have performances that equal those of conventional propellant compositions.
Exemplary embodiments of the invention are shown in the drawing in one-dimensional form
Fig. 1 represents a uniform distribution in the mass,
Fig. 2 shows the same constituents as in FIG. 1
but with a non-uniform distribution, Fig. 3 represent these same constituents, according to another
form of realization
Fig 1 shows a uniform distribution of grains within the composition. In a polyurethane foam 1 are ammonium nitrate granules 2 and, with a certain spacing 3, grains 4 of a nitramine such as octogen.

Given the alternating arrangement of these constituents, a homogeneous distribution is achieved, forming the ideal conditions for the combustion of these constituents, progressing in the direction of the arrow 5. The foam 1 in the intervals 5 exerts a retarding effect on a grains of nitramine
Fig. 2 represents, contrary to FIG. 1, a non-homogeneous distribution of granules 2 and grains 4 in the foam 1.

During combustion in the direction of the arrow 5, the grains 4 of nitramine in the upstream zone 6 react faster than the granules 2 in the median zone 7. Which is decisive in this way, egest the highest speed Reaction of the grains 4 with respect to the granules 2. The foam 1 situated in the intervals 3 between the grains 4 slows the reaction of these grains 4 in the zone 6.

 In zone 8, on the right, appears a lump 9 consisting of grains 4. These grains are in contact with each other. This results in zone 8, a faster reaction than in zone 6. The pressure peak that could possibly occur is neutralized by the surrounding foam 1.

Tests have shown that, thanks to appropriate mixing methods, the critical diameter of the nitramine is not reached or even approached. The balance between the retarding effect of the foam and that of the critical diameter (formation of lumps) can be adjusted so that no excessive reaction occurs.

 Fig. 3 represents a composition in which the grains 4 are entirely coated with a layer of ethylcellulose.

This resistant and waterproof layer is free of bubbles It ensures a minimum spacing between the grains 4 of a 9 lumps, while exerting a retarding effect. In the lumps 9, the set of layers 10 prevents the occurrence of a peak pressure during the reaction. This ensures a speed as a normal reaction.

The following table shows a comparison between a propellant composition known from German Pat. No. 28 09 279 and six compositions according to the present invention. In all cases, the density is 0.8 g / cm3
Column 1 indicates the content of nitramine,% by weight,
column 2 the ammonium nitrate content,% by weight,
column 3 the polyurethane content, x by weight,
column 4 the particle size of the nitramine, in mm,
column 5 the reaction energy, in kJ / g
column 6 the surface of the nitramine, in cm 2 / g.

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<tb><SEP> previous <SEP> 80 <SEP> - <SEP> 20 <SEP> 3J00 <SEP> 16.84
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<tb><SEP> 1) <SEP> 2 <SEP> 35 <SEP> 45 <SEP> 20 <SEP> A0.8 <SEP> 3460 <SEP> 11.05
<tb><SEP> 2) <SEP> 42 <SEP>. <SEP> 25 <SEP> 57 <SEP> 18 <SEP>, 1.0 <SEP> 3600 <SEP> 6.31
<tb><SEP> 3) <SEP> 20 <SEP> 63 <SEP> 17 <SEP> N0.6 <SEP> 3830 <SEP> 8.42
<tb><SEP> 4) <SEP> 15 <SEP> 69 <SEP> 16 <SEP> 0.5 <SEP> 4030 <SEP> 6.32
<tb><SEP> 5) <SEP> 4 <SEP> 10 <SEP> 67 <SEP> 20 <SEP> v0.4 <SEP> 3650 <SEP> 6.32
<tb><SEP> 1 <SEP> 10 <SEP> 67 <SEP> 20 <SEP> c0.3 <SEP> 3650 <SEP> 7.21
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In the direction of the arrow 12, the compositions exhibit an increasingly lively behavior.

In the direction of arrow 13, they exhibit an increasingly slow behavior
The compositions described with reference to FIGS. 1 to 3 may be adapted, by a suitable choice of parameters, to constitute propellant charges for artillery ammunition as well as for pyrotechnic ejector devices.

Claims (7)

1. Propellant charge compositions for ammunition of all  calibres and for pyrotechnic ejector devices,  containing a plastic foam with a density of 0.5 to 1.2  g / cm3 with one or more secondary explosive substances,  It is important that the proportion of foam  plastic, such as polyurethane foam, is 15 to 25%  by weight, the proportion of secondary explosives is 5 to  35% by weight, whereas these compositions contain in  in addition to 40 to 80% by weight of ammonium nitrate granules  of different sizes adapted to the size and method of use  with a particle size of 0.8 to 2 mm. 2. Propulsive compositions according to claim 1, characterized  in that the specific surface area of the nitramine fraction  is 6 to 12 cm2 / g. 3. Compositions according to claim 1, characterized in that  the secondary explosive is coated with a compact waterproof layer  and bubble-free, made of plastic or inert material,  0.3 to 1% by weight, based on the weight of explosive  secondary. Compositions according to claim 1, characterized in that  the nitramine fraction is one or more  defined particle size fractions. 5. Compositions according to claim 1, characterized in that,  for a relatively strong propellant charge with a density  of 0.8 g / cm 3, the nitramine fraction is 35% by weight with  a particle size close to 0.8 mm, the amine nitrate fraction  monium is 45 t by weight, and the foam fraction is 20%  in weight. 6. Compositions according to claim 1, characterized in that,  for a relatively slow charge with a density of 0.8 3  g / cm, the nitramine fraction is 10 g by weight with a  particle size close to C, 4 mm, the fraction nitrate uninoni-  um is 67 t by weight and the foam fraction is 20%  in weight. 7. Propellant compositions according to claim 3, characterized  in that the coating layer (10) of the explosive grains  secondary is made of polyurethane, ethylcellulose, lacquer  polyester and, with regard to the inert material,  graphite, wax or aerosil.