US3390636A - Electro-initiating device - Google Patents

Description

y 2. 1968 w. E. PERKINS ET. AL 3,390,636

ELECTRO-INITIAT ING DEVICE Filed Nov. 17, 1966 WILLIAM E. PERKINS GEORGE F? CATRAMBONE United States Patent 3,390,636 ELECTRQ-INITTATING DEVICE William E. Perkins, Runnemede, N.J., and George P. Catrambone, Warminster, Pa., assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 17, 1956, Ser. No. 595,275 11 Claims. (Cl. 10228) ABSTRACT OF THE DISCLOSURE A device for initiating an explosive which will be insensitive to initiation by radio frequency radiations or electro-static discharges. The device includes an electrode, housed in a metallic body, adjacent an iniziating means composed of carbon (graphite), red phosphorus (stabilized) and barium nitrate.

The invention described herein may be manufactured and used by or for the Government of governmental purposes without the payment to us of any royalty thereon.

This invention relates to an electro-initiating device and more particularly to an electro-initiating device which is insensitive to initiation by radio frequency and electrostatic discharges.

In prior art initiators, it is common to provide an electrical means for initiating an explosive which, in turn, ignites the main charge.

For more than a decade, ordnance items containing electro-explosive devices (EED) have caused deep concern because of malfunctions caused principally by RF radiations and electro-static discharges. These malfunctions have been manifested primarily by premature firing, by firing later than desired, and in some instances, misfiring.

Some early EED contained conductive priming compositions, but many of these were found to be too sensitive. One of the many approaches in solving this problem was to incorporate bridge wires in the BBB. It was found that the conductivity of the Wire had to be considered to cope with the RF problem, and even low-resistance bridge wires, safe enough to pass RF energies without firing, were dudded.

Limited success realized in bridge wired EED resulted in a shift to exploding bridge wired devices (EBWs). Although these EBWs were relatively safe to RF radiations, they could be actuated prematurely by electro-static discharges. This deficiency, and the fact that large power packages are required to fire them, has made them somewhat undesirable for ordnance applications.

Numerous other approaches have been considered; i.e., attenuators, filters, and auxiliary electrical device, but none olfer a complete solution and each add to the complexity and hence reduce the reliability of the BED.

The present invention describes conductive mix electric ignition element capable of functioning under service conditions of 65 F. to +350 F. from a prescribed firing pulse while being considered safe to inadvertent actuation from radio frequency (RF) signals and electro-static discharges.

It is therefore an object of the present invention to provide an electro-initiating device which is insensitive to initiation by radio frequency radiations.

Another object is the provision of an electro-initiating device which is insensiitve to initiation by electro'static discharges.

A further object is to provide an electro-initiation device utilizing a non-corrosive conductive composition.

Still another object is the provision of an electro-initiatice ing device for firing an explosive charge in response to an electrical impulse.

The above objects as well as others together with the benefits and advantages of the invention will be apparent upon reference to the detailed description set forth below, particularly when taken in conjunction with the drawing which shows a sectional view of the invention.

As can be seen in the drawing, an electro-initiating device 10 consists of a hollow cylindrical electrically conductive metallic body 12, which houses an electric conductor or electrode 14, an initiating charge 16 and a supplemental charge 18. Electrode 14 is composed of a metallic substance e.g., stainless steel, not readily oxidized over the operating temperature range. The initiating charge 16 is composed of carbon (graphite), red phosphorus (stabilized), and barium nitrate. The supplemental charge 18 could be an igniter, detonator or the like, depending upon the application of the device.

An electric insulator 20 is interposed between body 12 and electrode 14, and may be glass, ceramic or material of good dielectric and mechanical strength. A metallic support cup 22 houses supplemental charge 18 between a pair of retaining discs 24 and 26, the disc 26 being secured in body 12 by a crimp 28. Discs 24 and 26 may be magnesium, aluminum, or the like.

In operation, an electric current travels from a source (not shown) through a firing switch (not shown) into electrode 14. After the electrode 14, the current passes through initiating charge 16 thereby igniting the supplemental charge 18 through the retaining disc 24 and the main charge (not shown) of the ordnance item (not shown). The current then travels back through the conductive body 12 to the electrical source thereby com pleting the circuit.

As an example, the following requirements might be necessary in developing a bomb ejector cartridge having an EED which would:

(1) Be stable over the temperature range of 65 F. .to +350 F.

(2) Be capable of passing 1 ampere of current and/or watt for 5 minutes over the temperature range without firing.

(3) Be capable of firing prior or subsequent to conditions of (2) from a current of 5 amperes in less than 25 milliseconds.

(4) Be non-corrosive.

(5) Ignite propellant adequately.

(6) Exhibit an open circuit after firing to avoid drain on the power supply.

(7) Be safe from actuation via electro-static discharges.

The following combination meets the abovementioned desired requirements:

(1) Conductive mix-stabilized red phosphorus, 23% by weight, barium nitrate, 69.5% by weight, graphite, 7.5% by weight.

(2) Charge weight-3.5 grains.

(3) Loading pressure1500 psi.

(4) Conductive gap (shortest distance through the mix between the electrode and the body)0.20 inch.

(5) Resistance2.7 ohms +0.3 ohms (from R=E/I relationship at 1.0 ampere (for 5 minutes) over temperature range -65 F. to +350 F.).

(6) Functioning time-less than 25 milliseconds when fired at 5 amperes.

(7) Output-equivalent to primers containing 3.5 grams.

(8) Electro-static sensitivityinsensitive to discharge of 150,000 erges or less.

(9) Non-corrosiveness-equivalent to non-corrosiveness claimed for other red phosphorus/barium nitrate priming compositions.

t c 10) Open circuit requircmentswnen tired. the components are approximately as electrically conductive as the uncharged component.

An electric ignition element with satisfactory insensitivity characteristics to current RF and electro-static hazards has been attained using the non-obvious conductive miX approach.

The electro-initiating element will not prematurely function from electrical currents up to l.0 ampere tor periods of 5 minutes or less. With changes in iormulation, loading pressure. and gap widths the sensitivity characteristics can be altered to make the electro-initiating device more or less sensitive, l.e. no-tire current can be controlled at less than or more than l.0 ampere. Specifically, it has been established that increases in percentages of conductive material in the composition and an increase in the loading pressures tend to decrease sensitivity. while an increase in the gap width tends to increase sensitivity, i.e., fire at lower current levels.

The sensitivity of the electrode-initiating device IS a function of its conductivity.

Conductivity can be increased by increasing the graphite content, increasing the loading pressure. and/or decreasing the gap, and conversely, the conductivity can be decreased by decreasing the graphite content. decreasing the loading pressure, and/or increasing the gap distance.

Due to the negative temperature coetficient or sensitivity of graphite, compositions can be formulated which are more insensitive at higher temperatures and more sensitive at lower temperatures for use in unusual applications.

Obviously many modifications and variations or the present invention are possible in light or the above teachings. It is therefore to be understood. that within the scope of the appended claims. the invention may be practiced otherwise than as specifically described.

We claim:

1. In an electro-initiating device for detonating an emnance item having a main charge and comprising a hollow cylindrical conductive body having two epen ends,

an electrode housed in one of said ends.

a supplemental charge housed in the other or said ends.

and

initiating means within said body between 5310 electrode and said supplemental charge.

the improvement wherein said initiating means consists of a composition of stabilized red phosphorus. barium nitrate and graphite in such proportions as will not prematurely function from electrical currents up to 1.0 ampere for periods of five minutes max.

2. An electro-initiating device of the type described in claim 1 wherein said initiating charge is characterized by being insensitive to discharge of 150.000 ergs max.

3. An electro-initiating device of the type described in claim 1 wherein said initiating charge is characterized by 4 being stable over the temperature range of 65 F. to 350" F.

ll. An eiectro-initiating device of the type described in claim l wherein said initiating charge is non-corrosive.

it. An electro-initiating device of the type described in aim 1 wherein said initiating charge is characterized by insensitive to electro-static discharges.

An electro-initiating device of the type described in claim 1 wherein said initiating charge is characterized by being insensitive to radio frequency radiations.

I An electro-initiatirig device of the type described in claim 1. ivnerein said initiating charge consists of a composition or 13% by weight stabilized red phosphorus, t1i9.5% by weight barium nitrate and 7.5% by weight graphite.

ll. An eiectro-initiating device of the type described in claim l. wherein said supplemental charge is housed in .l metallic support cup and secured therein by a pair of retaining discs.

it. An eiectro-initiating device of the type described in im l. wherein said electrode is separated from said conductive body by an insulator thereby directing the current irom iald electrode to pass through said initiative charge before going out through said conductive body.

l0. An electro-initiating device of the type described in claim 3 wherein said electrode is composed of a metallic .itubstance not readily oxidized over said .temperature cringe.

Ill. An electro-initiating device comprised of c hollow cylindrical conductive body having two open ctids,

an electrode housed in one of said ends,

an insulator separating said electrode from said con- ..luctive body,

ct metallic support cup housed in the other of said ends,

ct pair of retaining discs secured in said metallic support cup.

.t supplemental charge housed in said pair of retaining cliscs.

initiating means within said body between said electrode crud said supplemental charge, comprised solely of a composition of about 23% by weight stabilized red hosohorus, b5% by weight barium nitrate, and

% by weight graphite.

lli leferences Cited UNITED STATES PATENTS llli.b45.57l c'l953 Silverstein 149-30 1.696.191 12;1954 Sheehan 10246 X Ii,320.l04 r'l967 Stadler et al 149-43 X .i DREIGN PATENTS 015.040 ll/1960 Great Britain.

lillENJAMIN A. BORCHELT, Primary Examiner.

W'ERLIN PENDEGRASS, Examiner.

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