Ammunition and explosives – Igniting devices and systems – Electrical primer or ignitor
Patent
1991-11-06
1993-10-19
Resan, Stevan A.
Ammunition and explosives
Igniting devices and systems
Electrical primer or ignitor
1022025, 428421, 428422, 428461, 428906, 524330, F42B 318
Patent
active
052535843
DESCRIPTION:
BRIEF SUMMARY
This invention relates to pyrotechnic materials, in particular but not exclusively suitable for use in pyrotechnic trains such as single and multi-train delay systems. The invention also relates to the use of such pyrotechnic materials in pyrotechnic trains.
It is well known that a wide range of pyrotechnic materials may be prepared in granular form by carefully selecting, preparing, and mixing together oxidising and oxidisable materials in specific ratios in order to achieve desired burning characteristics. Typical among such known granular combinations are oxidising polymers (such as fluoro-and chlorofluoro-hydrocarbon polymers) and oxidisable metals (such as magnesium), which in admixture are used as ignitors for propellant charges and as flare compositions for emitting infrared and smoke signals. Pyrotechnic compositions of this type are disclosed in, for example, U.S. Pat. Nos. 3,669,020 and 3,983,816 and U.S. Statutory Invention Registration H169.
Granular pyrotechnic compositions of the type consisting of polymer/metal mixtures suffer from a number of drawbacks. They are generally difficult to ignite, especially so when high energy ingredients are selected such as magnesium and polytetrafluoroethylene (PTFE). Great care must be taken in selecting ingredients of the correct particle size and shape, in mixing the ingredients in the correct ratio and in packing the composition to the correct density in a finished product since all these factors can have a considerable effect on burning characteristics. Such granular compositions can be extremely hazardous to handle, since they are liable to ignite spontaneously whilst undergoing formulation and further processing into end products. This necessitates clean room assembly conditions and the adoption of other elaborate and time-consuming safety procedures.
It is an object of the present invention to provide a pyrotechnic material whereby the aforementioned disdvantages of granular pyrotechnic compositions are overcome or at least mitigated in part.
According to the present invention, a pyrotechnic material comprises a substrate film of an oxidising polymeric material having vapour deposited thereon at least one layer of an oxidisable metallic material in at least one location on the surface of the substrate, the at least one layer being at least 2 microns thick and the said polymeric and metallic materials being conjointly capable of reacting together exothermically on ignition.
The advantage of vapour deposition is that it maximises molecular intermingling of the polymeric and metallic materials at their interface to provide a large, intimate and essentially void-free contact area between the two. The resulting pyrotechnic material exhibits considerable resistance to spontaneous ignition. Controlled ignition of the conjoint oxidising and oxidisable materials at any selected location initiates a self-sustaining, exothermic reaction between the two materials which progresses laterally along the interface. Intimate interfacial contact is further enhanced by the nature of vapour deposition processes which are conventionally conducted in essentially oxygen-free environments such as a vacuum or a low pressure inert atmosphere, so preventing the formation of an inhibiting film of metal oxide between the metallic and polymeric materials. This in turn renders the present pyrotechnic material easier to ignite than its granular counterparts. Furthermore, vapour deposition ensures that the advantageous properties of the polymeric substrate starting material (such as flexibility, strength, and toughness) are not substantially degraded during the manufacture of the pyrotechnic product.
The substrate may be made from one or more of a variety of polymeric materials which are preferably pliant. To enable an exothermic reaction to occur between the metallic material and the substrate, the polymeric material must contain an atom chemically bound to the polymer structure that is capable of oxidising the metal, and suitable atoms include halogens (which are preferred, especia
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Resan Stevan A.
The Secretary of State for Defence in Her Britannic Majesty's Go
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