EP1275930B1 - Pyrotechnical ammunition safety igniter acting in case of slow heating of the ammunition - Google Patents

Description

The present invention is in the field general pyrotechnic munitions, plus particularly in the field of explosive ordnance.

It particularly relates to a safety igniter for a pyrotechnic munition element comprising a envelope-shaped structure and a loading pyrotechnic substance contained in the structure, said igniter being intended to generate combustion without detonation of the pyrotechnic charge when the element ammunition is subjected to slow heating.

Thermal stresses such as kerosene or propellant fires, overheating indirect, are likely to lead to ammunition who undergo them to react pyrotechnically.

Ammunition elements loaded with explosives such missile heads, bomb bodies, penetrators and submarine ammunition can lead to violent reactions, deflagration or detonation, because of their strong confinement.

To reduce these reactions to an acceptable level, that is to say a simple combustion without projection of dangerous fragments, it is known to use a composite explosive loading based on binders inert or energetic polymers loaded with octogen (HMX), hexogen (RDX), nitroguanidine, perchlorate ammonium, triaminotrinitrobenzene (TATB), oxynitrotriazole (ONTA) and / or aluminum in combination with a system for deconfining the structure of the munition.

The deconfinement system may consist of opaque leaflets at a preset pressure which play the role of safety valve by releasing a evacuation surface to generated decomposition gases by the pyrotechnic reaction. Other techniques exist such as the use of fusible elements, cutting cords or rupture primers.

This security concept works perfectly for intense kerosene fires. In that case, the very high temperatures are communicated to the wall ammunition, then to the cargo that reacts in combustion at the interface structure / explosive as soon as the temperature exceeds the self-ignition temperature of the explosive, which is generally between 200 ° C and 240 ° C. The decomposition gases then move towards evacuation surfaces.

The case of less intense solicitations and long life is more complex.

The so-called slow heating solicitation (slow Cook Off) is classically specified and consists of subject a munition item to a warm-up a few degrees per hour until his reaction pyrotechnic that can intervene after several dozens of hours. These reactions can be very violent because they start in some cases in the heart pyrotechnic material, in a medium that will have the time to degrade by pyrolysis of the binder and start of chemical decomposition of active ingredients.

Heart starts are frequently observed with the large caliber ammunition (bombs, penetrators, submarine ammunition). They are there consequence of the thermally insulating nature of explosive and early exothermic decomposition at within the material. The heat released can not evacuate to the outside and generates an elevation additional internal temperature that accelerates further decomposition to the bulk reaction. The larger the dimensions, the lower is the reaction temperature.

A simple deconfinement system such as those mentioned in this case is insufficient to limit the overall level of reaction.

It is known to limit the level of reaction under conditions of slow heating, to insert, neighborhood of the deconfinement device, an igniter safety that reacts by burning at a temperature less than the reaction temperature of the load principal of the pyrotechnic munition, combustion of the igniter resulting in combustion without detonation of the main cargo.

Nos. 5,786,544 (which describes the preamble of claim 1) and GB 2,313,653 describe such safety igniters, essentially consisting of a plastic tube containing a powder or ignition pellets. The igniter is drowned in a foam ring that separates it from the load, in the rear part of the ammunition element, proximity to deconfinement holes.

The ignition pellets contained in the tube preferably consist of a mixture of boron and of barium chromate. However, it turns out that chromate barium is particularly toxic, carcinogenic, and that it causes heritable genetic damage. Of more, under thermal stresses, it emits fumes also very toxic.

Other solutions concerning the nature of ignition pellets are proposed, but none are really satisfying.

The use of propellant pellets nitrocellulose nitroglycerin double base present by example of nitroglycerin migration problems to storage with the pyrotechnic risks that this causes.

There is therefore, for the person skilled in the art, a need safety igniter to ensure the function previously described but not showing disadvantages such as those mentioned above.

The present invention proposes a solution to this problem and is mainly concerned with a new security igniter for ammunition element pyrotechnic comprising a shaped structure envelope and a solid pyrotechnic charge contained in the structure, said igniter being intended to generate combustion without detonation of the load pyrotechnic when the ammunition element is subjected to a slow warm-up.

This new safety igniter according to the invention is characterized in that it comprises a block in solid composition based on pentrite, and in that it is solely constituted by such a block.

Such a safety igniter is particularly simple to manufacture and insert into the element of ammunition. Monobloc, it presents properties intrinsic mechanics sufficient not requiring inert housing such as a plastic tube.

In addition, this block in solid composition based on pentrite is a detonable material bringing energy additional in the context of normal use of the ammunition, which is not the case of the aforementioned igniters of the state of the art that are not detachable. This duality of function, security igniter in the part of a slow and explosive heating in the frame of normal use of the ammunition, which is specific to the present invention is particularly advantageous.

It should also be noted that the constituents of the safety igniter according to the invention are neither toxic or carcinogenic, and that fumes from combustion are not particularly toxic.

It is known in the state of the art, to use solid compositions based on pentrite as a priming relay for explosive ordnance. The PCT patent application WO 99/53264 describes for example a such use which is unrelated to that of safety object of the present invention. This known use priming relay deterred even the skilled person to consider the use of these compositions based on pentrite in the safety igniter function previously described.

In the context of the present invention, it is necessary understand, by "slow" heating, a warm-up between 0.5 ° C / h and 50 ° C / h, preferably included between 1 ° C / h and 20 ° C / h, better still between 2 ° C / h and 10 ° C / h, for example about 3 ° C / h or 4 ° C / h.

By composition based on pentrite, it is necessary to otherwise include a composition having a weight in pentrite ≥ 5%, better still ≥ 10%, and better ≥ 25%, the maximum weight content being about 98%.

According to a preferred variant of the invention, the block in solid pyrotechnic composition based on pentrite is a composite explosive (cast plastic bonded explosive). Composite explosives are, so general, well known to those skilled in the art. They are obtained from binder explosive compositions plastic implemented by casting and then polymerization and consist of a loaded plastic binder containing at least one nitrated organic explosive charge like hexogen, octogen or pentrite. Other charges may also be present, oxidizing as example ammonium perchlorate, or reducing as for example aluminum.

Specifically, to prepare the block in explosive composite based on pentrite used as a lighter according to the invention, the first pentrite, and possibly the other charges, explosive or non-explosive, with a resin liquid polymerizable and optionally a plasticizer, then the paste is poured into a mold desired dimensions for the block. We then do polymerize the paste. Depending on the choice and setting of crosslinking agents, catalysts, wetting agents, composite explosives are obtained varied.

The mold may consist of a machined cavity in the pyrotechnic charge solid ammunition that we want to secure.

According to a preferred variant, the plastic binder is a polyurethane binder, the content of which is preferably between 12% and 20% by weight relative to the weight total of the composite explosive. Among the binders polyurethanes, those obtained by reaction are preferred of a polybutadiene hydroxylated with a polyisocyanate.

Other types of binders can be used, in particular silicone binders and polyester binders.

According to another variant of the invention, the block solid pyrotechnic composition based on pentrite is a compressed explosive, ie a binder explosive plastic implemented by compression. The matter of base (molding powder) consists of granules in which the charges are coated with a material thermoplastic according to a well-known technique of the skilled person.

After heating the molding powder to a temperature such that the thermoplastic binder begins to soften, it is introduced into a heated mold and then compressed under high pressure, of the order of ³ bar.

According to another variant of the invention, the block solid composition based on pentrite is an explosive cast-melted, for example a pentolite (mixtures of TNT and pentrite), such as pentolite 20-80 (20% weight of pentrite and 80% by weight of tolite) and the pentolite 50-50.

Cast-melted explosives, which are well known those skilled in the art, are implemented by pouring into molds of a suspension of a granular explosive in a melted explosive, such as TNT.

According to another variant of the invention, the block solid composition based on pentrite is a pentocire, that is, an essentially constituted composition of pentrite coated with a film of wax such as beeswax or synthetic wax.

The coating method, for example underwater, is well known to those skilled in the art.

The weight content of wax is preferably between 2% and 12%. Such compositions can also include additives such as graphite and / or aluminum.

The implementation of pentocires is carried out by cold pressing in the mold of a press.

In the context of the present invention, the block solid pyrotechnic composition based on pentrite can have some form.

Preferably, the block is in the form cylindrical, and better still in the form of a cylinder of revolution usually having a diameter between 2mm and 50mm.

The diameter of the block can be smaller, equal or greater than the critical diameter of the composition pyrotechnics based on pentrite constituting the block.

The height of the cylinder can be any. We usually uses diameter / height ratios included between 0.5 and 3, but preferably this ratio is neighbor of 1 or greater than 1.

It was surprisingly found that the temperature of reaction of the safety igniter, when the element of ammunition is subjected to slow heating, is a decreasing function of the block diameter, and that one can so very easily predetermine the temperature of reaction of the safety igniter depending on the diameter of the block, for a given composition and a given diameter / height ratio.

This particularly easy temperature setting reaction of the safety igniter offers an advantage significant to change the safety margins of a given ammunition, or to use similar igniters composition in ammunition with pyrotechnic charges of different compositions.

The present invention also relates to a pyrotechnic munition element comprising a envelope-shaped structure, generally metallic and for example steel, a solid pyrotechnic charge contained in the structure, a device for deconfinement of the structure, for example a system as mentioned above, and a safety igniter also as mentioned above and object of the present invention to generate combustion without detonation pyrotechnic charge when ammunition item is subject to slow heating.

The solid pyrotechnic charge contained in the structure is preferably explosive. In this case, the explosive charge is preferably an explosive composite but it can also be for example a compressed explosive, a cast-melted explosive for example tolite base, or an explosive-wax.

The solid pyrotechnic charge contained in the structure can however be a propulsive load, for example a solid propellant, preferably a composite propellant.

Whether the load is propulsive or explosive, the safety igniter allows, in situation of slow heating, to generate combustion without detonation of the cargo but also without propulsion the ammunition element, structure or fragments of structure.

According to a preferred variant of the invention, the safety igniter is located near the deconfinement device of the structure, so as to facilitate the escape of the combustion gases.

According to another preferred variant of the invention, the igniter is at least partially embedded in the solid pyrotechnic charge. For this, we can example machine in the loading a housing for igniter. Such housing can also be realized during the manufacture of molding loading using a removable core. The igniter is then placed in housing. A collage can be realized to promote the maintenance of the igniter in the housing.

One can also, and preferably, during the manufacture of the loading by molding, insert the safety igniter into the explosive dough after its casting and before its polymerization. After polymerization of the paste, the safety igniter is thus perfectly solid with the load.

The igniter may also not be at least partially embedded in the load, ie being independent of loading. It can be for example maintained in the structure using usual fasteners, or even drowned in a foam located in a chamber for the expansion of gases near the deconfinement device.

According to the present invention, when the element of ammunition is subjected to slow heating and that the temperature reaches the reaction temperature predetermined safety igniter, this one ignites. Hot gases and resulting particles of the igniter's combustion then initiate the burning of the ammunition load that burns without detonate or propel the ammunition element, the structure or structural fragments.

The present invention also relates to a process for generating combustion without detonation of a solid pyrotechnic charge content in the envelope-like structure of an element of pyrotechnic ammunition when subjected to a slow heating, said ammunition element comprising a deconfining device of the structure and a safety igniter as mentioned above according to the invention who, during the slow warm-up, reacts by simple combustion at a temperature below the temperature reaction of the pyrotechnic charge and then generates the combustion without detonation of the pyrotechnic charge.

Figures 1 and 2 show a section schematic longitudinal of 2 ammunition elements approximately cylindrical according to the invention.

• une structure 1 en forme d'enveloppe métallique approximativement cylindrique,
• un élément 2 métallique permettant la fermeture de la munition,
• un dispositif 3 de déconfinement de la structure 1,
• un chargement 4 pyrotechnique solide contenu dans la structure 1 et revêtu par ladite structure 1,
• un allumeur de sécurité 5 constitué d'un bloc cylindrique en composition pyrotechnique solide à base de pentrite,
• une chambre 6 d'expansion des gaz.

According to these two figures, the ammunition element comprises:

• a structure 1 in the form of an approximately cylindrical metal envelope,
• a metallic element 2 allowing the closure of the ammunition,
• a device 3 for deconfining the structure 1,
• a solid pyrotechnic charge 4 contained in structure 1 and coated with said structure 1,
• a safety igniter 5 consisting of a cylindrical block made of solid pyrotechnic composition based on pentrite,
• a gas expansion chamber 6.

According to the variant shown in FIG. 1, the igniter 5 cylindrical safety device is totally embedded in the loading 4, one of its 2 circular flat faces constituting part of the wall of the chamber 6.

According to the variant shown in FIG. 2, the igniter 5 cylindrical security is located in room 6, stalled by a ring of polyurethane foam no shown in the figure.

The following nonlimiting examples illustrate the invention and the advantages it provides.

Examples 1 and 2 Safety igniters according to the invention, composite explosive based on pentrite.

According to these 2 examples, the igniters present themselves in the form of a cylindrical block of revolution having a diameter of 30mm. The height of the block is 15mm for example 1 and 30mm for example 2. The mass of the lighter is 17g for example 1 and 34g for example 2. The composite explosive constituting these 2 igniters consists of 40% by weight of octogen, 44% by weight of pentrite and 16% by weight of a binder polyurethane based on polyoxypropylene triol and isophorone diisocyanate.

To get these 2 blocks, we first mixed powdery pentrite and octogen with alcohol then the isocyanate is added. We then poured the dough obtained in 2 molds of appropriate dimensions, then the paste was cured at 60 ° C.

These igniters have no toxicity particular, especially in case of contact with the skin. The flue gases are not dangerous. We can just notice in the subject an irritation of ocular and respiratory mucosa (tearing, cough), with no medium or long term sequelae on the health.

Example 3 Explosive ammunition element type indenter according to the invention.

We realized, according to the usual techniques well known to those skilled in the art, a penetrator of 280 kg, of a 285mm caliber, including a structure approximately cylindrical steel and 85 kg of a composite explosive charge consisting of octogen, ammonium perchlorate and aluminum as fillers and a polyurethane binder based on polybutadiene hydroxyl and isophorone diisocyanate as crosslinking agent.

This indenter has been equipped with a device decontainment of the structure consisting of operculas flappers, and on the other hand the safety igniter obtained according to Example 1, according to a provision in conformity to that schematized figure 1.

The safety igniter was inserted, during the carrying out the loading, in the explosive paste after its casting and before its polymerization, so that is perfectly attached to the load.

This indenter also comprises a gas expansion chamber 250 cm ³ volume, arranged as in Figure 1.

This indenter was subjected to a warm-up 3.3 ° C per hour, using a suitable oven.

When the temperature reaches 142 ± 4 ° C, an ignition of the safety igniter followed by a reaction of simple combustion of the loading of the ammunition, without fragmentation or propulsion of the structure. The value of 142 ° C corresponds to the average of 10 thermocouples installed in different positions of the oven.

A numerical simulation shows that without igniter security, a reaction of unknown intensity would have produced at an oven temperature of about 208 ° C.

Examples 4 to 6 Elements of explosive ammunition for use large caliber submarine according to the invention. Example 4

We realized, according to the usual techniques known to those skilled in the art, an ammunition element explosive for underwater use, 500mm caliber, comprising an approximately cylindrical structure steel and 150kg of a composite explosive charge consisting of hexogen, ammonium perchlorate and aluminum as fillers and a polyurethane binder to hydroxyl polybutadiene base and isophorone diisocyanate as crosslinking agent.

This ammunition was equipped with a device decontainment of the structure consisting of operculas flappers, and on the other hand the safety igniter obtained according to example 2, according to a compliant disposition to that schematized figure 1.

The safety igniter has been inserted into the loading as described for Example 3.

This munition also comprises a gas expansion chamber 400 cm ³ volume, arranged as in Figure 1.

This element of explosive ordnance was subjected to underwater use at a slow heating of 3.3 ° C by hour, using an appropriate oven.

When the oven temperature reaches 147 ° C, finds an ignition of the safety igniter followed by a reaction of simple combustion of the load ammunition, without fragmentation or propulsion of the structure.

Another test, made from an element of ammunition rigorously identical but lacking of safety igniter, leads, when the temperature oven reaches 188 ° C, a violent reaction of combustion, with fragmentation of the structure and projection of fragments beyond 15m.

Examples 5 and 6

• pour l'exemple 5, l'allumeur de sécurité a un diamètre de 80mm et une hauteur de 80mm.
• Pour l'exemple 6, l'allumeur de sécurité a un diamètre de 5mm et une hauteur de 5mm.

For each of these examples 5 and 6, an explosive ordnance element identical to that of Example 4 was produced except that:

• for example 5, the safety igniter has a diameter of 80mm and a height of 80mm.
• For example 6, the safety igniter has a diameter of 5mm and a height of 5mm.

During the same slow warm-up for example 4, there is an inflammation of the igniter when the oven temperature reaches 130 ° C for example 5 and 170 ° C for example 6.

In both cases, this inflammation of the igniter is followed by a simple combustion reaction of the loading of the ammunition, without fragmentation nor propulsion of the structure.

Claims (9)

1. Safety igniter (5) for a pyrotechnic munitions element comprising a structure (1) in the form of an envelope and a solid pyrotechnic charge (4) contained in the structure (1), said igniter (5) being intended to cause the combustion without detonation of the pyrotechnic charge (4) when the munitions element is heated slowly, i.e. at a rate of between 0.5°C/hour and 50°C/hour, characterized in that said igniter (5) consists solely of a block made of a solid pyrotechnic composition based on pentrite.
2. Safety igniter (5) according to Claim 1, characterized in that the block made of a solid composition based on pentrite is a composite explosive.
3. Safety igniter (5) according to Claim 1, characterized in that the block made of a solid pyrotechnic composition based on pentrite is in the form of a cylinder of revolution with a diameter of between 2 mm and 50 mm.
4. Pyrotechnic munitions element comprising a structure (1) in the form of an envelope, a solid pyrotechnic charge (4) contained in the structure, a device for deconfining the structure (1) and a safety igniter (5) for causing the combustion without detonation of the pyrotechnic charge (4) when the munitions element is heated slowly, i.e. at a rate of between 0.5°C/hour and 50°C/hour, characterized in that the safety igniter (5) is an igniter according to Claim 1.
5. Pyrotechnic munitions element according to Claim 4, characterized in that the solid pyrotechnic charge (4) contained in the structure (1) is an explosive charge.
6. Pyrotechnic munitions element according to Claim 4, characterized in that the solid pyrotechnic charge (4) contained in the structure (1) is a propellant charge.
7. Pyrotechnic munitions element according to Claim 4, characterized in that the safety igniter (5) is located near the device (3) for deconfining the structure (1).
8. Pyrotechnic munitions element according to Claim 4, characterized in that the safety igniter (5) is at least partially embedded in the solid pyrotechnic charge (4).
9. Process for causing the combustion without detonation of a solid pyrotechnic charge (4) contained in the structure (1), in the form of an envelope, of a pyrotechnic munitions element when the latter is heated slowly, i.e. at a rate of between 0.5°C/hour and 50°C/hour, said munitions element containing a device (3) for deconfining the structure (1) and a safety igniter (5) which, during the slow heating, reacts by simple combustion at a temperature below the reaction temperature of the pyrotechnic charge (4), and then causes the combustion without detonation of the pyrotechnic charge (4), characterized in that the safety igniter (5) is an igniter according to Claim 1.

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