US3789762A - Device to prevent accidental ignition of electro-explosives from electrostatic discharge - Google Patents

Abstract

Conductive structure connected to a electroexplosive device casing and extending into close proximity to igniter electrical lead wires at a place where discharge of stray electrostatic charges across a spark gap from one or both of said lead wires to the conductive means will not cause ignition of the electroexplosive devices.

Description

Unite- Staes FROM ELECTROSTATIC DISGE Inventor: John T. Petrick, Fredericksburg,

The United States of America as represented by the Secretary of the Navy, Washington, DC.

Filed: Mar 30, 1972 Appl. No.: 239,527

Assignee:

References Cited UNITED STATES PATENTS 8/1961 Franklin 102/28 @gggtf 19 [11] 3,78,762

Petrick Feb. 5, 1974 [5 DEVICE TO PREVENT ACCIDENTAL 3,264,989 8/1966 Rucker 102/28 IGNH'ION 0F ELECTRO EXPLOSIVES 3,333,538 8/1967 Schnettler 102/28 FOREIGN PATENTS OR APPLICATIONS 538,331 3/1957 Canada ..102 28 768,486 2/1957 Great Britain ..102/28 Primary ExaminerVerlin R. Pendegrass 57 ABSTRACT Conductive structure connected to a electroexplosive 2 Claims, 9 Drawing Figures PAIENIEDFEB 5W4 3;?89J'62 SHEET 2 UP 2 FIG. 7 F/G. 6

T0 PULSE FIRING GENERATOR 40 TO EED LEADS\ FIG. .9

DEVICE TO PREVENT ACCIDENTAL IGNITION OF ELECTRO-EXPLOSIVES FROM ELECTROSTATIC DISCHARGE BACKGROUND OF THE INVENTION A. Field of the invention The present invention relates generally to electroexplosive devices and more particularly to means to prevent electrostatically caused discharges from accidentally igniting electroexplosive devices.

B. Description of the prior art.

Previous methods for eliminating the electrostatic hazards to electroexplosive devices have generally been aimed at producing less sensitive devices. There are, however, many weapons in use today which necessitate the use of more sensitive electroexplosive devices. Thus, handling of these weapons and especially the handling of the sensitive electroexplosive devices is a hazardous operation.

The concept of discharging electrostatic charges by a spark gap from an electrical lead to the electroexplosive device casing is well known, but the structures heretofore used to accomplish this result are, for the most part, too complex, and cannot be added to existing electroexplosive devices without extensive modifications to the electroexplosive devices.

SUMMARY OF THE INVENTION The invention provides a simple and versatile means to prevent electrostatic charges from accidentally igniting electroexplosive devices.

OBJECTS OF THE INVENTION An object of the present invention is to render sensitive electroexplosive devices safe from inadvertant ignition due to static electricity without drastically changing the electroexplosive device design.

Another object is to provide means for making sensitive electroexplosive devices safe which is easily adaptable to existing electroexplosive devices.Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of an electroexplosive device utilizing a first embodiment of the present invention;

FIG. 2 is a front view of FIG. 1;

FIG. 3 shows the foil tab of the first embodiment before it is employed on an electroexplosive device;

FIG. 4 is a side view of FIG. 3;

FIG. 5 is a top view of a second embodiment of the present invention;

FIG. 6 is a front view of FIG. 5;

FIG. 7 is a front view of a third embodiment of the present invention;

FIG. 8 is a side view of FIG. 7; and

FIG. 9 is a cross-sectional view of a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show an electroexplosive device having a casing 18 which contains an explosive mixture in the lower part thereof. Lead wires 11 and 12 leading through an insulating Plug 17 into the explosive mixture are are connected thereat by a bridge-wire l9. Foil tab 13 has a conductive foil with conductive adhesive 14 on one side thereof as shown in FIG. 4. The foil tab 14 is originally flat as seen in FIG. 3. When applied to electroexplosive device 10, the adhesive is stuck to plug member 17 and is folded down at 13 to touch casing 18, as best illustrated in FIG. 2. Static charges are thereby conducted from the foil tab 13 to the casing 18 or vice versa. Lead wires 11 and 12 have bare spots, not shown, where the insulation has been removed at spark gaps 15 and 16 adjacent the pointed portions of foil 13.

The metallic foil typedevice provides electrostatic discharge protection by allowing an electrostatic discharge, characterized by a high voltage transient accompanied by a spark, to pass from one lead wire to the other by means of a spark occurring at the gaps 15 and 16 as shown in FIG. 1. Also, protection for an electroexplosive device having an electrostatic discharge passing through both wire leads 11 and 12 is given by sparks occurring at the same gaps, l5 and 16 in FIG. 1, which short circuits the electrostatic discharge to the electroexplosive device casing 18. Since at notime does the discharge pass through the electroexplosive device bridge-wire 19 or explosive mixture, there is .little chance for the electroexplosive device to initiate.

The embodiment of FIGS. 5 and 6 shows an electroexplosive device 20 which has a casing 28 with an explosive mixture in the bottom portion thereof. Leads 21 and 22 extend through insulating plug 27 and connect with bridgewire 29 which is incontact with the explosive mixture. Threaded needle points 23 and 24 are threaded into the insulating plug 27 preferably through casing 28. Needle points 23 and 24 are electrically grounded to casing 28 in any suitable fashion such as mere contact. Lead wires 21 and 22 have the insulation removed at the point nearest needle points 23 and 24, that is at spark gaps 25 and 26.

The needle point type device provides electrostatic discharge protection by allowing an electrostatic discharge to pass from one lead to another by means of sparks occurring in the spark gaps 25 and 26 as seen in FIG. 5. This device also protects an electroexplosive device having an electrostatic discharge passing through both wire leads 21 and 22 by sparks occurring at gaps 25 and 26 which short circuit the electrostatic discharge to the casing 28. Therefore, no discharge passes through the bridge-wire 19 or the explosive mixture so the electroexplosive device cannot be accidentally fired by static electricity.

FIGS. 7 and 8 show another embodiment of the present invention wherein an extension 32 at one end of electroexplosive device casing 31 is an integral part of the casing. Once an insulating plug with lead wires extending therethrough is placed-in the top of electroexplosive device 30, as in the previously discussed embodiments, tab extension 32 is folded over so that pointed portions 33 and 34 are near the lead wires to form a spark gaps therebetween. The lead wires, not shown, as in the other embodiments, have insulation removed near pointed portions 33 and 34 of extension 32 at the spark gaps, not shown. The function of this embodiment is the same as in the previous embodiments discussed above.

FIG. 9 is a remote protective device embodying the present inventive concept. Lead wires 41 and 42 pass through insulating block 57 and extend to the electroexplosive device lead wires. Wire 43 is connected to needle point 44 and to the electroexplosive device metal casing ground. The remote protective device 40 of FIG. 9 may be placed at any reasonable distance from the electroexplosive device associated therewith. Metal discharge needle 45 is pointed at both ends and is fixed by any suitable means, such as a set screw, so as to form spark gaps 46 and 47 when lead wires 41 and 42 are inserted in the insulating block with the insulation removed at the point adjacent the needle point. Partially threaded upper discharge needle 44 is adjacent lead wire 41 and forms a spark gap 48 between the point of needle 44 and the closest portion of lead wire 41 where the insulation has been removed, though the missing insulation is not illustrated in the drawing.

Obviously many modifications and variations of the present invention are possible in light of 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.

What is claimed is:

1. In an electroexplosive device having a casing and a pair of lead wires connected by a bridge wire in a body of explosive material, the safety improvement comprising:

an exteriorly disposed electrically conductive foil member connected to said casing by an electrically conductive adhesive and having pointed portions thereof adjacent said lead wires to form spark gaps between said lead wires and said foil member, wherein said spark gaps are insulated from said explosive material.

2. The device of claim 1 wherein said spark gaps are insulated by an insulating member received in said casing.

Claims (2)

1. In an electroexplosive device having a casing and a pair of lead wires connected by a bridge wire in a body of explosive material, the safety improvement comprising: an exteriorly disposed electrically conductive foil member connected to said casing by an electrically conductive adhesive and having pointed portions thereof adjacent said lead wires to form spark gaps between said lead wires and said foil member, wherein said spark gaps are insulated from said explosive material.

2. The device of claim 1 wherein said spark gaps are insulated by an insulating member received in said casing.

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