US3278353A - Ammunition priming composition comprising aromatic hydroxy compounds - Google Patents

Description

United States Patent 3,278,353 AMMUNITION PRIMING COMPOSITION COM- This invention relates to priming compositions, and more particularly to such compositions intended for electrical ignition in military firearms such as aircraft machine guns.

An electric primer composition, like any other primer composition, has as its principal ingredients a material which functions to start the reaction, an explosive to propagate the reaction, a fuel to maintain the reaction, and an oxidizer for that fuel. In the electric primer, the material which starts the reaction is one which is sensitive to the heating and other effects of an electric current. At one time, electric primers made wide use of bridge wire heating devices for electric firing, but current practice eliminates the bridge wire and utilizes the mixture itself as an electrically conductive element.

In mixtures of this kind, the conductivity of the mixture is generally brought within the desired limits by the addition of controlled amounts of graphite, carbon black, acetylene black or metallic powders. When an electric current is passed through such a mixture, there appears to be a two-fold effect, that of resistance heating of the bulk of the mixture and that of probably localized electrostatic discharges and arcing.

In a typical primer composition of this type, both graphite and powdered zirconium are present and add conductivity to the mixture. The reaction probably starts as the result of the dual effect, mentioned above, on the finely powdered zirconium which will burn violenly under the action of an electric spark when in the presence of an oxidizing agent. Either natural flake, natural amorphous or synthetic graphite may be used with equal efficiency.

In a typical electric priming composition, PETN (pentaerythritoltetranitrate) or a similar explosive material is included as the explosive element and serves to increase the heat of the reaction and to propagate that re action to the fuel which ignites the propellant.

In the same typical priming compositions, the fuel may be a metallic powder or a material like calcium silicide. If a metal powder is used it is generally but not necessarily of larger particle size than the metallic powder serving to start the reaction. The oxidizing agent for the fuel is frequently one or both of such compounds as lead peroxide and/ or barium nitrate. Where a coarse powder, such as coarse zirconium powder or calcium silicide, is used as a fuel, the fuel burns with a high heat of reaction and is "ice projected in incandescent particle form through the propellent charge to produce particularly effective ignition.

The composition described thus far has been exten sively used and in its use it has been determined that proportions of graphite or acetylene black which yield a low electrical resistance through the pellet are desirable to reduce the sensitivity of the mixture to ignition by static electrical charges. It is known that an electrical resistance which is too low requires too high a current to cause consistent ignition and leads to other troubles as a result of contact resistances, etc., at other portions of the electrical circuitry. It is also known that one of the primary objectivesof.theelectrical primer will not be achieved unless the percussion sensitivity of the mixture is kept low.

In general it may be said that a primer which has an electrical resistance of less than 1000 ohms across the pellet is desirable, but that current consumption will be too high unless the electrical resistance is above 50 ohms. Inspection limits on an exemplary electric primer class as acceptable to those primers having a resistance between and 500 ohms but for most purposes the wider range of 50 to 2000 ohms is entirely satisfactory.

Percussion sensitivity will be adequate if the primer (1) will withstand the conventional drop test of a 1 pound weight dropped from a height of 20 inches or (2) will withstand the double feed test in the appropriate machine guns, or (3) will not fire when subjected to the impact of a firing pin in conventional machine guns adapted to percussion firing.

We have discovered that we can substantially increase the electrical resistivity of an electric primer composition without sacrifice of igniting or explosive efiiciency by the addition to the mixture of small amounts of aromatic hydroxy compounds, such as phenol, and particularly the nitro derivatives of such compounds, such as TNR also known as styphnic acid (2,4,6-trinitroresorcinol), 2,4-dinitroresorcinol, 2-mononitroresorcinol, 4-mononitrophenol, 2,4-dinitrophenol, or picric acid (2,4,6-t1'initrophenol). Since these compounds are themselves explosives they may contribute usefully to the heat developed in the reaction and certainly do not detract from the effectiveness of the composition. It also appears that these additives have the effect of stabilizing the resistance level of the primer and in avoiding changes in resistance as a function of aging of the mixture.

The principal object of this invention is to reproducibly control the electrical resistance of electric primers without detracting from their explosive efliciency, and other objects and advantages may be discerned from a study of the following detailed description.

Examples of the use of such a resistance controlling agent are found in Examples II et seq. Example I is included for background as a typical mixture which does not include such an additive agent.

Example I II III IV V VI VII VIII Powdered zirconium, coarse 32.5 parts 32.5 parts 32.5 parts 32.5 parts-. 32.5 parts..- 32.5 parts-.- 32.5 parts.

Powdered zirconium, fine. 7.5 parts 7.5 parts 7.5 parts... 7.5 parts 7.5 parts. 7.5 parts. 7.5 parts.

Lead peroxide, granular 20. 20.0 parts 20.0 parts- 20.0 part 20.0 parts 20.0 parts 20.0 parts.

Barium nitrate 20. 20.0 parts. 2 par 20.0 parts-.- 20.0 parts 20.0 parts, 20 20.0 parts. 200 parts 20.0 parts-.- 20.0 parts.-- 20.0 parts.

Graphite 2.0 parts... 2.5 par 2.0 parts. 2.5 parts 2,0 parts,

2,4,6-trinitroresorcinol 2,4 dinitroresorcinol 2-mononitroresorcinol 2,4,6-trinitrophenol 2,4-dinitrophenol 4-mononitroph Electrical Resistance, Average-.. 375 ohms. 1,890 ohms 176 ohms. 300 ohms. 200 ohms 205 ohms.

Eleetristatic Sensitivity Low Low cw Low Low Low.

Percussion Sensitivity Low Low Low Low Low Low.

Primers prepared from the mixtures of Examples II et seq. have shown adequate and consistent electrical sensitivity and for test purposes are required to fire 100% when subjected to the discharge of a 2-mfd. electrical capacitor charged to a nominal voltage of 160 volts. Under service conditions, such primers are fired from a 4-mfd. capacitor charged to 250 volts. At the same time, such primers have shown satisfactory characteristics in regard to their sensitivity to static electrical discharges and percussive blows.

The exact reason for the efiect of these additives is not known. In part, it may be mechanical, since these additions tend to dilute the mixture, and, in part, their effects may be due to their chemical properties, it being noted that a free OH group is present in each additive cited as an example. In either case, their properties are such as to contribute usefully to the heat of the reaction and to at least avoid any decrease in explosive force as a result of the dilution of the mixture.

Although certain specific examples are shown herein, it should be understood that the invention should not be considered to be limited to those examples or to the proportions set forth therein except as set forth in the appended claim, which is to be broadly construed.

What is claimed is:

An ammunition priming composition for electrical ini- 4 tiation consisting of the tabulated ingredients in proportions substantially as follows:

References Cited by the Examiner UNITED STATES PATENTS 2,771,034 11/1956 Blake 524 BENJAMIN R. PADGETT, Acting Primary Examiner.

WILLIAM G. WELE, ROBERT L. CAMPBELL, LEO-N D. ROSDOL, O. R. VERTIZ, Examiners.

L. A. SEBASTIAN, Assistant Examiner.