EP0036810B1 - Process for charging a pyrotechnic delay unit - Google Patents

Description

The technical sector of the present invention is that of pyrotechnic devices intended to fulfill various functions, for example of delay, ignition, lighting, tracing, gas or smoke generator, etc. These devices consist of a pyrotechnic chain comprising several superimposed elements. These elements each have their own role and must transmit the phenomenon to the next element in the chain. They consist of mixtures known as pyrotechnic compositions placed in a metal support such as for example a tube.

These mixtures include different solid compounds and are formulated by considering the function they must fulfill: primary or secondary explosives, oxidants, metals or reducing compounds, various additives intended either to promote mixing, or to give the composition specific properties such as than electrical conduction, thermostability or sensitivity to certain actions.

However, they must also respond to other practical constraints of use, among which are: homogeneity and reproducibility of the proportions, flowability with a view to volumetric dosing, generally of industrial type, insensitivity to external humidity and above all safety both of the mixing process and of the implementation operations.

The manufacture of a pyrotechnic device involves the establishment, or loading, of the elements of the pyrotechnic chain and is done by introducing in the pulverulent solid state quantities perfectly dosed by volume or by mass of each pyrotechnic composition which must be previously shaping.

It is already known, in current industrial practice, that the simple dry mixing of several solid compounds, crystallized or not, more or less hygroscopic, of different real densities, of spread out granulometry and often very fine, is sometimes difficult if not impossible.

However, various granulation processes are known for obtaining homogeneous mixtures of several solid compounds which can be used industrially. These methods mostly involve the introduction into the mixture of an addition substance acting as a binder. Such a process is described in patent FR-A _No. 2046583.

• - mélange à sec des composés pulvérulents,
• - granulage mécanique à travers des grilles,
• - enrobage avec un liant.

The shaping of these mixtures can therefore be done in several ways:

• - dry mixing of the pulverulent compounds,
• - mechanical granulation through grids,
• - coating with a binder.

• - homogénéité difficile à assurer et entraînant soit une impossibilité de dosage, soit une dispersion trop grande dans le fonctionnement pouvant aller jusqu'au raté,
• - sensibilité des compositions à l'hygrométrie extérieure compromettant leur dosage et leur stabilité ultérieure,
• - taux de rebut important imposant des opérations supplémentaires de tri par tamisage ou des refontes de certaines fractions,
• - accidents ou incidents dus à une excitation inopinée de la composition au cours d'opérations mécaniques sur des compositions sensibles.

The methods chosen, for each of the elements of the pyrotechnic chain, often have a certain number of drawbacks among which we can cite:

• - homogeneity difficult to ensure and resulting in either an impossibility of dosing, or too great a dispersion in the operation which can go as far as failure,
• - sensitivity of the compositions to external humidity compromising their dosage and their subsequent stability,
• - high scrap rate requiring additional sorting operations by sieving or recasting of certain fractions,
• - accidents or incidents due to unexpected excitation of the composition during mechanical operations on sensitive compositions.

In addition, in the particular case of a pyrotechnic chain for an igniter plug, of a grenade for example, successively comprising an ignition composition, a pyrotechnic delay and possibly a reinforcing or uncorking composition, the simultaneous implementation, in particular in an automatic loading machine, these various solid compounds is tricky. In fact, the ignition compositions are sensitive to friction and to heating and have a particle size and a nature which make them slightly hygroscopic, while the pyrotechnic compositions playing the role of delay are mechanically less sensitive but imply perfect homogeneity and a great regularity of loaded mass.

The present invention provides a pyrotechnic device of the latter type, having an easier loading process, in particular in an automatic machine for loading ammunition, and which has improved characteristics of reproducibility, aging and performance, while eliminating the aforementioned drawbacks specific to the known shaping of the various constituents of a pyrotechnic chain.

• - chargement de la totalité de la composition d'allumage,
• - chargement d'environ 20% de la composition à retard,
• - compression avec un poinçon conique sous environ 1900 bar,
• - chargement d'environ 60% de la composition à retard,
• - compression avec un poinçon conique sous environ 1900 bar,
• - chargement du reste de la composition à retard, puis de la composition renforçatrice.
• - dernière compression avec un poinçon plat sous environ 1900 bar.

The subject of the invention is also a method for loading a pyrotechnic module of the type comprising, successively, mixtures of pulverulent compounds consisting of an ignition composition, a delay composition, and, optionally, a reinforcing composition, characterized in that it comprises the following successive stages:

• - loading of the entire ignition composition,
• - loading of approximately 20% of the delay composition,
• - compression with a conical punch under approximately 1900 bar,
• - loading of approximately 60% of the delay composition,
• - compression with a conical punch under approximately 1900 bar,
• - loading of the rest of the delay composition, then of the reinforcing composition.
• - last compression with a flat punch under approximately 1900 bar.

The invention therefore allows the production of a pyrotechnic chain by dosing successively, and in particular volumetrically, in the pulverulent state, of compositions obtained by various known shaping methods, in particular by the process for coating pyrotechnic substances described in French patent No 2309493.

• - mise en solution diluée d'un polymère d'enrobage dans un solvant, ionique ou non, à raison d'une concentration en poids de 2 à 20%,
• - introduction de 10 à 60% en poids de la composition pyrotechnique pulvérulente à enrober, sous agitation convenable pour maintenir une dispersion homogène des particules,
• - addition progressive sous agitation d'un ou plusieurs polymères antagonistes liquides ou visqueux pour lequel le solvant précité a une affinité plus grande que pour le polymère d'enrobage précédent, jusqu'à obtenir une concentration en poids comprise entre 20 et 60% du poids total,
• - filtration pour séparer les grains plastifiés de la phase liquide résiduelle, puis lavage de ces grains,
• - enfin, séchage pendant quelques heures de ces grains, à l'air libre ou en étuve.

It will be recalled that this process makes it possible to obtain directly, without prior mixing, without mechanical operation which is a source of incidents, without sorting at the outlet, a pyrotechnic composition, in particular of ignition or delay, homogeneous, reproducible, of perfect flowability and of reduced hygroscopicity. It basically includes the following steps:

• - dissolving a coating polymer in a solvent, ionic or not, at a concentration by weight of 2 to 20%,
• introduction of 10 to 60% by weight of the pulverulent pyrotechnic composition to be coated, with suitable stirring to maintain a homogeneous dispersion of the particles,
• - gradual addition with stirring of one or more liquid or viscous antagonistic polymers for which the abovementioned solvent has a greater affinity than for the preceding coating polymer, until a concentration by weight of between 20 and 60% by weight is obtained total,
• - filtration to separate the plasticized grains from the residual liquid phase, then washing of these grains,
• - finally, drying these grains for a few hours, in the open air or in an oven.

Likewise, the granulation of the delay composition can be carried out in a known manner, by introduction of the composition into a planetary mixer, of a binder and of at least one solvent, until suitable wetting of the composition and obtaining of '' a fluid and homogeneous paste. After drying, this paste is introduced into a rotary granulator actuated from a distance. The granule obtained is spread and dried, then sieved between 80 and 200 μ, to obtain a granulated retarding composition suitable for industrial loading.

Finally, and in a known manner, the reinforcing or uncorking composition is prepared by simple dry mixing with the rotary mixture.

This pyrotechnic module, intended to equip for example mines, torpedoes, destruction charges, can be manufactured in large series, without hygrometry constraint, using weight or volumetric loading machines, and has a great regularity. of operation, good reliability and good aging behavior, as shown below.

• - 130 mg de composition d'allumage enrobée selon le procédé décrit dans le brevet français N_o 2309493,
• - 70 mg de composition à retard granulée selon un procédé mécanique connu, puis en comprimant avec un poinçon conique sous une pression de 1900 bar,
• - 200 mg de composition à retard granulée comme ci-dessus, en effectuant ensuite une nouvelle compression à 1900 bar, puis ajoutant:
• - 70 mg de composition à retard granulée comme ci-dessus,
• - 100 mg de composition renforçatrice mélangée au mélangeur rotatif.

By way of nonlimiting example, the unit loading of 30 modules with pyrotechnic delay is carried out by successively introducing into each tube placed in a matrix the following compositions, after weighing with a precision balance:

• - 130 mg of priming composition coated by the method described in French Patent _No. 2,309,493,
• - 70 mg of granulated retard composition according to a known mechanical process, then by compressing with a conical punch under a pressure of 1900 bar,
• - 200 mg of granulated retard composition as above, then performing a new compression at 1900 bar, then adding:
• - 70 mg of granulated retard composition as above,
• - 100 mg of reinforcing composition mixed in the rotary mixer.

A final compression is then carried out with a flat punch under a pressure of 1900 bar.

The finished tubes are then fitted with a percussion primer. Their fall shooting with delay measurement gives the following results: average delay time of 5.8 s with a standard deviation of 0.18 s.

The following table makes it possible to compare the results obtained by pyrotechnic modules loaded with pyrotechnic compositions variously shaped by the known methods mentioned above. The series of modules were subjected for 4 d to a relative humidity of 100% at 35 ° C., then taken out of the oven, primed and drawn with the fall sheep. All the modules include a single reinforcing composition which is simply dry mixed.

Claims (1)

1. A method for loading a pyrotechnic delay module of the type comprising, successively, mixtures of compounds in powder form consisting of an ignition composition, a delay composition and, possibly, a reinforcing composition, characterized in that it comprises the following successive steps:

   - loading of all the ignition composition,

   - loading of about 20% of the delay composition,

   - compression with a conical punch under a pressure of about 1,900 bar,

   - loading of about 60% of the delay composition,

   - compression with a conical punch under a pressure of about 1,900 bar,

   - loading of the rest of the delay composition, followed by the reinforcing composition,

   - a last compression with a flat punch under a pressure of about 1,900 bar.