US3728967A - Tri-pri three contact primer - Google Patents

Abstract

The present invention discloses a balanced electrically initiated primer directed toward use in a cartridge having a conductive mix electrical primer but could also be used with bridgewire electrical primers. Dielectric material is placed around the explosive primer mix, forming a capacitor configuration which prevents inadvertent initiation of the electroexplosive device.

Description

United States Patent 1191 Hinklle et a1.

1 11 3,728,967 14 1 Apr. 24,1973

[5 1 TRl-PRI THREE CONTACT PRIMER 3,320,889 5/1967 HOltZ ..102/28 x D 3,333,538 7/1967 Schnettler ..102/28 [75] Inventors. Charles J. Hmkle, Fredencksburg, 3,363,565 1/1968 Walther 102/46 X5 4 f Mal'quardt, Alexan- 3,524,408 1/1968 Pierson ..102/28 r1a, a.

FOREIGN PATENTS OR APPLI AT! [73] Assignee: The United States of America as C 0N8 represented b th Secretary f th 805,118 11/1958 Great Britain ..102/46 Navy Primary ExaminerRobert F. Stahl [22] Flled: June 1969 Attorney-Edgar J. Brower, Arthur L. Brarming, [21] APPL NuZ 835,896 Thomas 0. Watson, Jr. and Jack C. Berenzweig [57] ABSTRACT [52] U.S.Cl ..102/46 I 5 l 1 int Cl Fnb 9/08 The present mvennon discloses a balanced electrically [58] Fie'ld 28 702 initiated primer directed toward use in a cartridge having a conductive mix electrical primer but could also be used with bridgewire electrical primers. [56] References Cited Dielectric material is placed around the explosive UNITED STATES PATENTS primer mix, forming a capacitor configuration which prevents inadvertent initiation of the electroexplosive 319.628 6/1885 Russell ..102/46 deviw 3,196,041 7/1965 McNulty et al... .102/28 X 3,308,758 3/1967 Stadler et al. 102/28 2 Claims, 4 Drawing Figures A. I v \8 a J. I r J a Pmmm wn y L 3.728.967 sum 1 [IF 2 INVENTORS CHARLES J. Hl/V/(LE FRANK R. MAROUARDT ATTORNEY TlRlI-PIRI THREE CONTACT PRIMER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to electrically initiated primers and, more particularly, to improved safety devices to prevent electrically initiated ammunition from being inadvertently actuated by radio frequency energy.

Description of the Prior Art Electrically initiated primers, both the conductive mix and wire bridge varieties, are vulnerable to initiation by inadvertent application of stray energy. The commonly used configuration of devices known as the unbalanced configuration, having a single hot terminal and a case ground return, are more susceptible to initiation by stray energy than are those having firing circuits isolated from ground. Those devices having a single hot terminal are particularly susceptible to stray energy initiation because of the unbalanced electrical configuration and low energy requirements for firing. In the case of wire bridge devices the problem is ameliorated by designs requiring large amounts of energy for their functioning. The problem of suitable protection for conductive mix devices has never been adequately solved. Radio frequency filters and shielding are commonly used methods of preventing inadvertent initiation electroexplosive devices. These methods cannot ordinarily be successfully applied to small individual devices such as gun cartridges, while at the same time permitting ready handling and utilization. During handling of these items the only protection ordinarily provided is that afforded by the energy requirement of the device itself and the care and attention given by handling personnel, directed toward avoiding accidental contact with the hot terminal of electroexplosive device. I

SUMMARY OF THE INVENTION The concentric arrangement of the dielectric and the isolation of the conductive mix from ground of the disclosed invention produces a near ideal capacitor. The use of this primer eliminates the need for radio hazard shielding presently used and minimizes the electromagnetic hazard in removing loaded cartridges from a jammed gun.

It is therefore an object of the present invention to provide a balanced electrical initiator.

A further object of the present invention is the provision of an electrical initiator which does not require any external shielding means.

A further object of the present invention is to provide an initiator which is immune to inadvertent actuation by radio frequency energy.

Other objects, advantages and novel features of the present invention will become apparent from the fol lowing detailed description of the invention when considered in conjunction with the accompanying drawings. I

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a greatly enlarged view in section of the detonator device of the instant invention in accordance with a preferred embodiment thereof;

FIG. 2 illustrates an end section of the device in FIG.

FIG. 3 shows the electrical schematic circuit of the device in FIG. I; and

FIG. 4 shows an alternative embodiment of the device wherein mechanical or electrical detonation is utilized.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. I, which illustrates the preferred embodiment, a threecontact primer having an open ended cylindrical dielectric insulator 3 enclosing an explosive mix 6. Insulator 3 is partially enclosed by a U-shaped conducting ring sleeve assembly 4. The second opening of insulator 3 is closed by conducting button 7. The capsule formed by ring sleeve 4 and button 7 is enclosed by a second dielectric insulator 5 having a lower dielectric constant than insulator 3. This completely electrically insulates the capsule from the cartridge case 8 into which it is inserted.

.FIG. 2 shows an end view of the three-contact primer of FIG. 1. FIG. 3 shows the electrical schematic equivalent of the device in FIGS. 1 and 2. Capacitor 33 is the symbolic representation of dielectric insulator 3. By a suitable choice of dielectric materials and/or spacing, capacitor 33 designed to provide a capacitance in shunt with explosive mixture 6, such that its value is greater than the capacity of capacitor 35. Capacitor S is the schematic representation of dielectric insulator 5 while resistor 36 represents the explosive mixture 6 of FIG. 1. The primer is initiated solely by application of a firing voltage between the button 7 and the ring sleeve assembly 4.

Referring again to FIG. 1, the dielectric material of insulator 3 may be preformed material of the titanium family. In order to conserve space, materials having a high dielectric constant are preferred. By proper choice of spacing, dielectric constant and the area of the capacitor plate material, the design can be optimized for manufacture. The dielectric material of insulator 5 is not critical but should have a lower dielectric constant than insulator 3. The dielectric breakdown voltage rating of capacitors 3 and 5 should be in the order of 600 volts or greater. The loss tangents of these insulators are not a critical factor but should not be excessive in order to prevent heat buildup in the capacitors.

FIG. 4 shows an alternative use of the three-contact primer wherein mechanical detonation may be used. Washer 13 comprises the high dielectric constant insulator. This washer is the full functional equivalent of dielectric insulator 3 in FIG. ll. U-shaped primer body 14, equivalent to ring sleeve 4 of FIG. I, surrounds washer l3 and primer mix 6. Conductor button 7 is placed across the U-shaped opening insulating material 15 and the entire device is enclosed in cartridge case 8 as before. When a large pressure is applied to button 7 by the firing pin of a gun, not shown, the primer mix is compressed against an anvil 9 and an explosion occurs.

The geometry of the metal parts of the design of three-contact primer is dictated by size limits of the expected usage of the primer. Their exact shape can also vary depending upon ease of manufacturing, so long as the capacitive voltage divider concept is physically maintained.

The advantages of these balanced electrical circuit configurations are threefold:

1. For a given current, the series configuration of capacitors 3 and 5 limits the total voltage drop which may appear between the primer button and cartridge case in inverse proportion to the value of the equivalent capacitance, where C equiv. (C 5)/ C5)- 2. The voltage across the conductive mix is dependent upon the capacitance ratio of C /C Making this ratio large decreases the voltage across the conductive mix.

3. Firing energy must be applied to two contacts, neither of which grounded to the case and both of which are small in total surface area thereby preventing inadvertent firing Obviously many modifications and variations of the present'invention are possible in the light of the above teachings.

What is claimed is: 1. A three-contact explosive initiating device safeguarded from inadvertent firing comprising a primer capsule, said capsule comprising an explosive mix;

a first cylindrical open ended insulating means surrounding said explosive mix;

a U-shaped conducting means surrounding said first insulating means whereby one end of said cylinder is closed;

a conducting button across said other end of said cylinder and electrically insulated from said U- shaped conducting means;

a second insulator having a lower dielectric constant than said first insulator, surrounding said primer capsule; and

a cartridge casing surrounding said second insulator whereby said primer capsule is electrically insulated from said cartridge casing.

2. The device of claim 1 wherein an anvil is inserted into said primer mix so as to allow percussion actuation of said device.

Claims (2)

1. A three-contact explosive initiating device safeguarded from inadvertent firing comprising a primer capsule, said capsule comprising an explosive mix; a first cylindrical open ended insulating means surrounding said explosive mix; a U-shaped conducting means surrounding said first insulating means whereby one end of said cylinder is closed; a conducting button across said other end of said cylinder and electrically insulated from said U-shaped conducting means; a second insulator having a lower dielectric constant than said first insulator, surrounding said primer capsule; and a cartridge casing surrounding said second insulator whereby said primer capsule is electrically insulated from said cartridge casing.

2. The device of claim 1 wherein an anvil is inserted into said primer mix so as to allow percussion actuation of said device.

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