US3661085A

US3661085A - Electrically actuated initiator

Info

Publication number: US3661085A
Application number: US859336A
Authority: US
Inventors: William M Smith; Thomas W Norton; John D Hawley
Original assignee: Ensign Bickford Co
Current assignee: Ensign Bickford Aerospace Corp
Priority date: 1969-09-19
Filing date: 1969-09-19
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

A fast response electrically actuated pyrotechnic or explosive initiator includes an initiating charge in contact with only those portions of a bridge wire located immediately adjacent the area of wire contact with the terminal posts.

Description

I United States Patent 1151 3,661,085 Smith et al. May 9, 1972 {54] ELECTRICALLY ACTUATED [56] References Cited INITIATOR UNITED STATES PATENTS 7 l t W'lli M. S th' Th W. N E 2] ms g fi' g? f gg 2,228,339 1/1941 Burrows et al ..102/28 Hanlandy a of Comm 2,717,204 9/1955 Noddin et al. l49/22 3,188,914 6/l965 Dahl ..102/28 [731 Asfignee: E Ens'gn'B'ckmd s'msburye 3,227,083 1/1966 Moses et al ..102/28 onn.

{22] Filed: Sept. 19, 1969 Primary Examiner-Verlin R. Pendegrass [21 1 pp No 859 336 Attorney-Prutzman, Hayes, Kalb & Chilton [57] ABSTRACT 52 v.s.c1 ..102/28 51 A fast response electrically actuated pyrotechnic or exploslve [58] Field at Search ..102/28 initiator includes an initiating charge in Contact with y those portions of a bridge wire located immediately adjacent the area of wire contact with the terminal posts.

7 Claims, 2 Drawing Figures ELECTRICALLY ACTUATED INITIATOR BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates generally to pyrotechnic and explosive initiators and is particularly concerned with a new and improved electrically actuated initiator of the type employing a bridge wire.

Electrically actuated initiators of both low and high energy, including detonators as well as igniters, are generally comprised of an elongated casing within which are positioned a pair of terminals joined by a bridge wire. One or more pyrotechnic or explosive charges are retained within the casing adjacent the wire for ignition thereby. An initiating or first charge positioned adjacent the base conventionally embeds or at least intimately contacts the entire bridge wire along its full length while a main sustaining charge of the device is conveniently located immediately in front of the initiating charge and at the output end of the device. An electric current applied across the terminals of the device causes the bridge wire to ignite the initiating or first charge which in turn sets off the main or sustainer charge of the device and provides the desired short duration output. Conventionally, initiators of this type exhibit an ignition time on the order of l to 2 milliseconds with a normal firing current of 2-6 amperes.

In accordance with the present invention there is provide an electrically actuated pyrotechnic or explosive initiator having a substantially faster reponse time than that exhibited by conventional initiators employed heretofore. Accordingly, it is a primary object of the present invention to provide a new and improved electrically actuated initiator having an ignition time of substantially less than I millisecond.

Another object of the present invention is to provide a new and improved initiator of the type described capable of decreasing the reaction time of the initiator by one full order of magnitude.

A more specific object of the present invention is the provision for an electric initiator structure wherein the pyrotechnic or explosive mix contacts only selected portions of the bridge wire, effecting a decrease in the heat transfer from the wire and a corresponding increase in the surface reaction within those selected portions where the ignition mix is in contact with the bridge wire.

Still another object of the present invention is to provide a compact and economical fast response electric initiator of the type described which produces the improved result indicated hereinbefore without sacrificing the reliability or durability of the initiator construction.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

These and related objects are accomplished in accordance with the present invention by providing an electrically actuated pyrotechnic or explosive initiator of the bridge wire type having an initiating charge in contact with only those portions of the bridge wire located immediately adjacent the area of contact between the wire and the terminal posts of the initiator A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawing which sets forth an illustrative embodiment and is indicative of the way in which the principle of the invention is employed.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a sectional view along the length of an electric initiator illustrating one embodiment constructed in accordance with the present invention; and

FIG. 2 is a sectional view of the initiator of FIG. 1 taken along the line 2-2 of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing in greater detail wherein like reference numerals indicate like parts throughout the figures, an electrically actuated pyrotechnic initiator is shown as comprising an elongated generally cylindrical cup-shaped casing 10 of relatively thin walled construction having an insulating plug or header 12 sealably secured within the open end thereof. A pair of electrically conductive terminal posts 1 4v extend through the plug in spaced parallel relationship terminating within the casing adjacent the innermost end of the plug. As can be appreciated, the header 12 can be made of suitable support material such as glass, ceramic, plastic, rubber of the like capable of securely and fixedly retaining the terminals in their proper relative positions. A thin filament or bridge wire 16 such as resistance wire extends between and is electrically connected to the ends of the terminal post within the casing. Generally wires exhibiting a resistance of about 1 ohm have been found to give satisfactory results.

An initiating or first charge 18 is disposed within the casing adjacent the header l2 and in intimate contact with the bridge wire 16. In the embodiment chosen for illustrative purposes, charge 18 takes the form of a centrally apertured compact disk with the diameter of the central aperture being approximately equal to the distance between the ends of the spaced terminal posts 14. Thus, as shown, the initiating charge is in intimate contact with the bridge wire 16 only within the area immediately adjacent the points of contact between the bridge wire and the terminal posts.

A primary or main charge 20 is positioned between the enclosed end of casing 10 and the initiating charge. It will be appreciated that the use of a main charge as well as its composition will vary depending on the type of device desired. Although only a single pyrotechnic or explosive main charge is shown, it also will be appreciated that multiple charges may readily be utilized. Regardless of the presence of a main charge or its composition or configuration, the central portion of the bridge wire should be free from intimate contact with the initiating charge of the device while the portion of the bridge wire adjacent the terminal posts should be contacted thereby. Thus, in an explosive detonator an appropriate initiating charge would contact the bridge wire in the manner illustrated and additional primary and secondary explosive charges would be compacted forwardly of the initiating charge. In the case of an igniter, the main or sustainer charge could be placed immediately adjacent the initiating charge on either end thereof relative to the output end of the device. Thus, it would be possible to use the construction described in copending US. Pat. application Ser. No. 773,808 filed Nov. 6, 1968 for a Pyrotechnic Igniter and assigned to the assignee of this application.

It is not intended that this invention be in any way limited by a specific theory of operation; however, it is believed that the improved ignition time acquired can be attributed at least in part to one or more of the following factors associated with the particular construction employed. Accordingly, the faster functioning time may be attributed to the fact that the air space around the central portion of the bridge wire decreases the heat transfer from that portion of the wire, facilitating a faster rate of heat increase within the wire particularly at the points of interconnection with the terminal posts. Further, the mass of metal and initiating mix at the terminal posts may cause localized hot spots when current is applied. In any event, the bridge wire is not required to heat an extended surface of the ignition mix along its entire length and regardless of the specific mechanism by which ignition takes place, it has bee found that the construction of the present invention provides a substantially faster reaction time. In fact, the reaction time is consistently faster by a factor of about 10 over conventional devices utilized heretofore.

The particular pyrotechnic and explosive charges utilized are those conventionally employed in such devices. For example, for igniters the charge or mix may comprise zirconium and potassium chlorate, boron and lead oxide or other similar metal-oxidizer deflagrating mixtures while detonators conventionally employ high explosives such as PETN as the main charge with a primer such as lead azide between the explosive and the ignition charge.

The following specific example is given as an illustration of the manner in which the present invention can be employed and is not intended to in any way form a restriction or limitation thereon.

EXAMPLE A number of electric igniters having an initiating charge of the construction shown in the drawing were assembled with a platinum-tungsten bridge wire having a diameter of 0.0017 inch and a length sufficient to provide a resistance of 1 ohm. Only an initiating charge was employed consisting of a 70/30 mixture of zirconium and potassium chlorate compacted to approximately 10,000 psi. The mix was compacted in the form of both a centrally apertured disk substantially as shown in the drawing and as a disk having no central aperture. A series of tests were run on these devices and the firing times measured. The results are set forth in the following table.

As can be clearly seen from the foregoing test results, the firing times for those devices made in accordance with the present invention were consistently faster by a factor of about 10 as compared to the times for devices of conventional design.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

We claim:

1. An electrically actuated initiator having an ignition time of less than 1 millisecond comprising a generally tubular casing, a pair of electrical terminals secured within the casing, a bridge wire having end portions electrically connected to the terminals within the casing and a central portion integrally connecting the end portions, and an initiating charge in intimate contact with the bridge wire within the area adjacent the end portion thereof and having a central cavity, the central portion of the bridge wire being positioned within said central cavity.

2. The initiator of claim 1 wherein the initiating charge is a centrally apertured pellet.

3. The initiator of claim 1 including a main charge positioned adjacent the initiating charge for ignition thereby.

4. the initiator of claim 1 wherein the initiating charge is a pyrotechnic material.

5. The initiator of claim 4 wherein the pyrotechnic material is a mixture selected from the group consisting of zirconiumpotassium chlorate and boron-lead oxide.

6. The initiator of claim 1 wherein the bridge wire has a resistance of about 1 ohm, the initiating charge is a centrally apertured compacted pellet consisting of a mixture of zirconium and potassium chlorate and the ignition time for the initiator is about 0.2 millisecond and less.

7. The initiator of clalm 1 wherein an air space IS provided around the central portion of the bridge wire.

Claims

5. The initiator of claim 4 wherein the pyrotechnic material is a mixture selected from the group consisting of zirconium-potassium chlorate and boron-lead oxide.

7. The initiator of claim 1 wherein an air space is provided around the central portion of the bridge wire.