Combustion Igniter Cord with Enhanced Power

The present invention relates to a combustion igniter cord with enhanced power.

The technical field of the invention is that of cartridges comprising a propellant charge housed in a case and of devices for igniting such propellant charges.

It is known to produce cartridges wherein the device for igniting the propellant charge comprises energetic igniter cords which extend between a means of initiation secured to a rear part of the case and the projectile. For example, U.S. Pat. Nos. 5,129,324, 5,179,250 and EP1092940 may be considered.

Igniter cords, in combustion and not in detonation, usually comprise a plastic tube containing a pyrotechnic composition such as black powder or a composition combining boron and potassium nitrate or and potassium perchlorate. Such cords are well known and described in particular by the patent FR2441598. In such a case, the power and the energy of the ignition are supplied exclusively by the pyrotechnic composition present inside the tube.

Igniter cords are used for the ignition of the propellant charge in a cartridge the projectile of which penetrates deep into the powder bed, more particularly for an arrow projectile with a long bar. Conventional axial ignitor tubes cannot be incorporated with such projectiles.

In known igniter cord cartridges, the cords extend between an axial igniter tube connected to the base and the case or the projectile. More particularly, in U.S. Pat. Nos. 5,129,324 and 5,179,250, the cords are arranged along the inner wall of the case and are held in place by plastic stars.

Mention may also be made of U.S. Pat. No. 3,320,882 which describes an igniter cord consisting of a continuous column of a mixture of lead azide and a particulate metal confined in a metal sheath.

As part of the increase in the performance of arrow shells, it is necessary to implement new propellant powders.

Unlike old powders such as single base (B19T) or double base (GB19T) powders, the new formulations have much lower ignitability. The energy and the power of the ignition system must therefore be substantially increased.

Energy is related to the quantity of pyrotechnic material related to the ignition, while the power is related to the time over which the energy is diffused in the propellant powder bed. Thereby, the problem posed by conventional igniter cords such as ITLX® cords is that same have a limited maximum amount of energy compared to the energy requirement to ignite the new propellant powders.

Furthermore, the increase in the quantity of pyrotechnic composition in the cord generally induces a decrease in the rate of combustion and thus a decrease in the speed of the cord. As a reminder, igniter cords have a combustion speed (˜500 m/s) unlike detonating cords. The drop in speed induces a drop in power where the need is to increase same.

The present invention proposes to solve such problems by proposing a combustion igniter cord providing in particular from 100 to 1000% compared with simple cords (e.g. ITLX®) in terms of ignition power, then serving to ignite new generations of propellant powders, which cannot be ignited by cords of the prior art.

The idea behind the present invention is to increase the amount of energy available while maintaining an operating time similar to the standard cord, hence increasing the power. The increase is achieved according to the invention by means of a relay loaded with propellant powder, e.g. of small or medium caliber. The standard cord can always be used because same is used to control the propagation speed of the ignition. The relay is used to significantly increase the energy delivered.

In order to facilitate the implementation of the relay, it is envisaged according to the present invention to implement an over-sheath around the standard cord in order to be able to fill the interstices thereby generated by the energetic material serving as a relay, e.g. powder of medium caliber. The connection between the over-sheath and the sheath of the standard cord can be made by means of one or a plurality of mechanical links. The materials of the sheath and of the over-sheath are made of plastic, but it is also possible to provide same as an extruded propellant powder energetic material.

The compatibility in terms of ignitability between the internal pyrotechnic composition and the relay, which consists of medium caliber powder or other pyrotechnic composition such as black powder, should be sufficient for the latter to be rapidly initiated in contact with the combustion products of the composition of the standard cord.

To this end, the present invention relates to a igniter cord for energetic ignition of a propellant charge contained in the case of a cartridge, said igniter cord consisting of a core comprising a pyrotechnic material and surrounded by a sheath, characterized in that the sheath consists of two concentric cylindrical tubes between which is arranged a free powder energetic material.

In a first embodiment, the two tubes are made of an inert polymer material, where said tubes can be connected together, e.g. by radial fins, the assembly being obtained by extrusion of the polymer material.

In a second embodiment, the two tubes contain a propellant powder energetic material extruded in one block.

In a third embodiment, one of the tubes is made of an inert polymer material and the other is made of an extruded energetic propellant powder material forming a block.

The inert material may be low density polyethylene.

Tubes containing an energetic propellant powder material extruded in a block may be solid or split tubes.

The energetic material may be chosen from single-base propellant powders, multi-base propellant powders and pyrotechnic compositions.

The single-base propellant powders may be chosen from nitrocellulose powders, such as same marketed by Milan Blagogevic-Namenska under the references NC-16 and NC-161, B7T from Nammo Vihtavuori and PCLs from PB Clermont.

Multi-base propellant powders can be chosen from NK1405 powders from Eurenco or PBC2000 from PB Clermont.

A pyrotechnic composition may be chosen from black powder, benite, a boron/potassium nitrate composition (B/KNO) and mixtures thereof.

The core may be made of a thermite including at least one metal chosen in particular from Al, Mg and B, an oxidizing agent chosen in particular from KNO, KClOand WO, and a binder chosen from polymers and nitrocellulose.

A comparison the times of ignition between a conventional cord having a plastic sheath enclosing an ITLX® core material and a cord according to the invention having a sheath formed of two concentric tubes containing extruded NC-16 propellant powder between which is located a spherical double-base powder such as PB Clermont PBC2000 powder, with the same core, showed a 5 times lower ignition time by means of the cord of the invention.