Mechanical shielding for electric primer

#This invention relates to a primer for cartridge casings for projectile ammunition, such as, but not limited to 20 mm Phalanx cartridges used by the military. Technology has long passed beyond percussion initiation of primers for shell cartridges having high rate of fire for military applications. Instead, primers containing pyrotechnic compositions are now electrically initiated. This initiation is accomplished by a relatively simple process of bringing a current-carrying plunger in the gun breech structure up behind the backside of the cartridge casing, once the cartridge is properly chambered, to electrically contact a button electrode therein for completing an electrical circuit through the primer button for initiating detonation of pyrotechnic composition in the circuit path. Detonation of the primer pyrotechnic composition in turn ignites propellant inside the cartridge casing.

#Electrical initiation of cartridge primers is now common practice. Usually an explosive pyrotechnic material is made conductive and sandwiched between a pair of electrical conductors inside the primer. Current is passed through the pyrotechnic material from one conductor to the other to generate a temperature rise in the material sufficient to initiate its detonation. The detonating pyrotechnic material in turn ignites propellant in the cartridge casing to propel a projectile forward.

#The electromagnetic environment aboard ships and aircraft, as well as on other military equipment, has increased substantially in recent years along with the increased use of electronic equipment. It is in this dense atmosphere of electromagnetic radiation that cartridges having electrically fired primers are stored, handled and used. High-power radar, for example, and communication equipment emit strong electromagnetic fields to the surrounding environment.

#FIG. 1 is side view of a 20 mm cartridge round with the base of the casing partially cut away to illustrate the location of the electric primer.

#FIG. 2 is a greatly enlarged cross-sectional view of the improved primer positioned in a cartridge recess with an electrode plunger adapted for making electrical contact to complete a firing circuit through the primer.

#FIG. 3 is a greatly enlarged cross-sectional view of a typical prior art primer in position within a cartridge casing, and with a finger of a human hand in contact with a button thereby completing a circuit for illustrating primer vulnerability to antenna coupling.

#For a setting in which the present invention is adapted for use, refer to FIG. 1, which is a partial cross-sectional view of a 20 mm cartridge 100 employing a sabot round 102. The aft end or base 104 of cartridge casing 106 is illustrated in cross-section to expose an electric primer, identified generally by the numeral 108, in position therein. Casing 106 is made of electrically conductive material such as brass, through which current flows when a circuit is completed for initiating detonation of pyrotechnic material in the primer.

#Refer now to FIG. 2 of the drawings where primer 108 is shown in greatly enlarged cross-sectional detail and positioned in a recess 110 formed in casing base 104. Primer housing 116, also formed of conductive material, is designed to physically retain several components making up the primer. Primer housing 116 is in the form of a cup having a cylindrical side wall and flat end or base wall 118 which is provided with an axially disposed small diameter opening 119 extending therethrough, preferably with a chamfered inlet 120. There is further illustrated in FIG. 2 a firing circuit. When plunger 112 is moved forward by a camming action (not illustrated), it completes a powered circuit 122 through the primer to initiate a pyrotechnic charge therein.

#Primer housing 116 is adapted to have its cylindrical side wall press-fitted or otherwise secured in cylindrical recess 110 in cartridge base 104 with its open end facing forward toward propellant (not illustrated) in the cartridge casing. A small axially disposed opening 123 is proved in base 104 for allowing the products of primer detonation to reach propellant forward in the casing.