US3208379A

US3208379A - Squib arrangement initiated by exploding wire

Info

Publication number: US3208379A
Application number: US90775A
Authority: US
Inventors: Herbert H Mckee; William F Green
Original assignee: Special Devices Inc
Current assignee: Special Devices Inc
Priority date: 1961-02-21
Filing date: 1961-02-21
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

Sept. 28, 1965 H. H. M KEE ETAL 3,208,379

SQUIB ARRANGEMENT INITIATED BY EXPLODING WIRE Filed Feb. 21, 1961 am w j 200 as I I 34 32 4Q Q F I G. 2.

WILLIAM F GREEN HEKBEIZT H. MCKEE INVENTORS Q BY W AGENT.

United States Patent 3,208,379 SQUIB ARRANGEMENT INITIATED BY EXPLODING WIRE Herbert H. McKee, Granada Hills, and William F. Green,

Van Nuys, Califl, assignors to Special Devices, Inc.,

San Fernando, Calif., a corporation of California Filed Feb. 21, 1961, Ser. No. 90,775 6 Claims. (Cl. 102-28) This invention relates generally to the squib art and, more particularly, to an improved arrangement for initiating squib operation in a secondary explosive filled squib.

The increase in utilization of relatively high direct current voltage and alternating current systems in aircraft and missiles has necessitated an increase in the no fire voltage level (the voltage level at which ignition will never occur) for squibs that are incorporated in explosive actuated devices associated with such aircraft and missiles. As a result, the always fire voltage level (the voltage level at which an ignition will always occur) has also increased. Further, safety criteria indicate that the use of primary explosives is not desirable in these applications. Therefore, it has become necessary to provide a squib having initiation circuitry that will not ignite a secondary explosive under the relatively high direct current no fire voltages and alternating current levels and yet positively ignite under the always fire voltage level. Further, it is also desirable that non-destructive tests of the squib initiation circuitry characteristics be conducted prior to utilization of the squib.

Prior arrangements have not always proven completely satisfactory in meeting all these requirements and yet still providing reliable ignition. A spark gap in the squib initiation circuitry has provided some measure of no fire safety but the squib may be prematurely actuated by radar energy and static electricity. In addition, a spark gap can not be check for gap separation or circuit resistance after assembly without exploding the squib. Other arrangements, which have incorporated only an exploding bridge wire in the squib initiation circuitry, have often been rendered subsequently inoperative by application of voltages which do not explode the bridge wire but only melt it.

Accordingly, it is an object of this invention to provide an improved squib.

It is a further object of this invention to provide a squib in which ignition is initiated by an exploding wire.

It is another object of this invention to provide an exploding wire squib that is insentive to electrostatic or radar energy pulses. 1

It is another object of this invention to provide an exploding bridge wire squib incorporating an electric gap in the squib initiation circuitry.

It is another object of this invention to provide an exploding bridge wire squib incorporating an electric gap in which non-destructive tests of the squib initiation circuitry properties may be made prior to utilization.

The above and other objects are realized in accordance with the principles of this invention by providing, in squib initiation circuitry, an electric gap in series with an exploding bridge wire means. In one embodiments of this invention a pair of electrically conductive leads extend inwardly, through a dielectric sealing means, to the interior of a secondary explosive filled case. Each lead is electrically isolated from the other lead and from the case. A fi st end of an exploding bridge wire is connected to a first of the leads on the interior of the case and the bridge wire is in direct contact with the secondary explosive. A second end of the exploding bridge wire is connected to an elec trically conductive, thin-walled, generally cylindrical sleeve surrounding at least a portion of the second lead that extends into the interior of the case. The sleeve is electri- 3,208,379 Patented Sept. 28, 1965 cally isolated from the second lead that it surrounds by dielectric spacers. The dielectric spacers are proportioned to provide a preselected, known gap between the sleeve and the second lead.

Upon application of a high voltage current pulse across the pair of leads, the gap between the sleeve and the second lead breaks down providing circuit continuity between the leads through the bridge wire. The high voltage current pulse explodes the bridge wire and the energy associated with the exploding bridge wire ignites the secondary explosive.

The invention is described in greater detail in the following specification taken together with the accompanying drawing, in which like reference characters are utilized for similar elements and in which:

FIGURE 1 illustrates the structures associated with one embodiment of this invention;

FIGURE 2 illustrates an arrangement for non-destructive circuit testing of this invention; and

FIGURE 3 illustrates another embodiment of this invention.

Referring now to FIGURE 1, there is shown a sectional view of a squib arrangement, generally designated as 10, according to the principles of this invention. The squib arrangement 10 comprises a generally cup shaped case means 12 in which

secondary explosives

14 and 16 are enclosed. The secondary explosive 14 may take the form of a consolidated grain and the secondary explosive 16 may be in the form of a loose grain to allow easier ignition. Alternatively, both secondary explosive 14 and secondary explosive 16 may be consolidated grains. Applicants have found that the secondary explosive PETN (pentaeryth-rite tetranitrate) has provided reliable operation in squib arrangements incorporating this invention.

The

secondary explosives

14 and 16 are sealed in case means 12 by a dielectric sealing means 18. Sealing between the dielectric sealing means 18 and case means 12 is preferably hermetic to insure that the operation of the squib 10 is unaffected by ambient humidity and pressure variations. This may be achieved by rolling and crimping the case means 12 to the dielectric sealing means 18, as shown on FIGURE 1, or other well-known sealing methods may be employed. The dielectric sealing means 18 may be glass, polyester resin, or the like. A pair of electrically conductive leads 20 and 22 extend through the dielectric sealing means 18 and have portions 20a and 22a, respectively, interior the case means 12 and

portions

20b and 22b, respectively, exterior the case means 12. The pair of

leads

20 and 22 are electrically insulated from each other and from the case means 12 by the dielectric sealing means 18.

An electrically conductive sleeve means 24 is electrically insulated from and maintained in voltage breakdown gap relationship to lead 22 by the dielectric spacers 26 and 28. The gap between the sleeve 24 and the lead 22 is selected to provide a voltage breakdown between the sleeve 24 and the lead 22 at a predetermined minimum always fire voltage.

An exploding bridge wire means 30 has a first end 30a connected in electric continuity relationship with the sleeve 24 and a second end 30b connected in electric continuity relationship to the portion 20a of lead 20.

In operation, a direct current source 32 is applied across the

leads

20 and 22 on their exterior portions 20b and 2211 through a low impedance gap switch 34. The voltage of the applied direct current source 32 is at least the always fire voltage. Under the influence of this voltage, there is a breakdown of the gap between the portion 22a of the lead 22 and the sleeve 24. When this voltage breakdown occurs, there is electric continuity between the lead 22 and the lead 20 through the exploding bridge wire means 30 and the resulting current pulse at the always fire voltage explodes the exploding bridge wire means 30 which ignites the secondary explosive 16. The ignited secondary explosive 16 ignites the secondary explosive 14- to provide squib operation.

The exploding bridge wire means 30 is selected so that a current pulse at the always fire voltage explodes the wire. While it is known that wires can be made to explode on application of a current pulse at a high voltage, the exact phenomena associated with an exploding wire reaction has not yet been precisely identified. The book Exploding Wires, edited by William G. Chace and Howard K. Moore, Plenum Press, Inc., 1959, based on the Conference on Exploding Wire Phenomenon, April 1959, presents several theories on the underlying mechanism of exploding wires. However, it is known that the energy release accompanying an exploding wire is great enough to ignite a secondary explosive, such as PETN. This permits the fabrication of reliable squibs that do not require a primary explosive such as fulminate of mercury or lead azide in their powder train.

In the squibs fabricated by applicants in accordance with the principles of this invention, the

leads

20 and 22 were formed from number 22, American Wire Gage (approximately 0.02535 inch outside diameter), quadruple Formvar coated, copper wire. The sleeve means 24 was formed from a section of Kovar tubing, a very low thermal expansion metal manufactured by Stupikofi Ceramic and Manufacturing Company, Latrobe, Pennsylvania, having an external diameter of 0.040 inch and an internal diameter of 0.030 inch providing a radial gap of approximately 0.0023 inch between the sleeve means 24 and the lead 22. The exploding bridge wire means was formed from two strands of 2 mil gold wire. These squibs were exposed to no fire voltages of 36 volt direct current and 110 volt, 60 cycle, alternating current and the squibs were not ignited nor was the initiation circuitry destroyed. When exposed to an always fire voltage of 2000 volt direct current, 1 microfarad capacitance, through a low impedance gap switch, the electric gap broke down and the exploding bridge wire 30 was exploded thereby igniting the secondary explosive 16, which was composed of less than 100 mesh loose pack PETN. This, in turn, ignited the secondary explosive 14 which was composed of less than 40 mesh PETN, consolidated to 15,000 pounds per square inch, thereby providing the desired squib operation.

In some applications, reliability considerations may require that a plurality of exploding bridge wire means, connected in parallel, be included in the squb initiation circuitry. Thus, as in the example above, two exploding bridge wires were provided between the sleeve 24 and lead 20. In such a configuration, each bridge wire is selected so that it explodes at the always fire voltage under the condition of only one exploded bridge wire intact and also under the condition of both bridge wires intact.

The squibs fabricated in accordance with this invention may also be checked, after assembly, for initiation circuitry continuity and resistance. One method of this testing is illustrated schematically in FIGURE 2. A high frequency, low voltage, signal source 36 energizes a capacitance resistance bridge 38 which has the squib 10 connected across one branch of the bridge. Any capacitance in the system may be nulled out by phase shift in phase and null detector 40. The high frequency signal passes through the gap between the sleeve means 24 and lead 22 to provide circuit continuity without exploding the exploding bridge wire means 30. Resistance of the initiation circuit is then read by standard balanced bridge techniques. For the particular squib described above, applicants have found that a signal at a frequency of approximately 1 megacycle and volts provides satisfactory testing.

In FIGURE 3 there is shown in partial section the structure associated with another embodiment of this invention. In this embodiment, a pair of electrically conductive leads 20 and 22' extend through a dielectric sealing means -18 to the interior of the squib 10. The leads 20 and 22' are electrically insulated from each other and also from the case means 12. An interior portion 22a of the lead 22' is hollowed out to provide a generally thin-walled section. A pair of

dielectric spacers

42 and 44 retain an electrically conductive pin means 46 within the hollowed out portion 22a electrically insulated from and in voltage breakdown gap relationship to the portion 22a of the lead 22. An exploding bridge wire means 30 is connected between the pin means 46 and an interior portion 20a of the lead 20. v

The operation of this embodiment is similar to the operation of the embodiment shown on FIGURE 1. When the always fire voltage is applied across the

leads

20 and 22, the gap between the pin means 46 and the portion 22a of the lead 22 breaks down. The resulting current pulse explodes the exploding bridge wire means 30 which ignites the secondary explosive 16. The secondary explosive 14 is thereby ignited to provide the desired squib operation.

There are many modifications and adaptations of this invention that may be devised by those skilled in the art. For example, the voltage breakdown gap may be provided in the squib initiation circuitry by a pair of flat plates with a dielectric therebetween. In addition, a completely redundant squib initiation circuitry may be provided, for reliability, by including two pair of leads fabricated in accordance with the principles of this invention. Therefore, the foregoing specification and the appended drawing are to be considered as illustrative only and the following claims are intended to cover all variations and adaptations that do not depart from the true scope and spirit of this invention.

Having thus described a new and improved squib arrangement, what is claimed as new and is desired to be secured by Letters Patent of the United States is:

1. In combination: a generally cup shaped case means; a secondary explosive powder train contained within said case means; a dielectric sealing means hermetically sealing said secondary explosive powder train in said case means; a first and a second electrically conductive lead extending through said dielectric sealing means and each of said leads having an interior portion inside said case means and each of said leads electrically insulated from each other and from said case means; an electrically conductive sleeve means in voltage breakdown gap relationship to said interior portion of said first lead and said sleeve means electrically insulated from said first lead, and defining a voltage breakdown gap therewith for breaking down at a preselected voltage to transmit an electric current at said preselected voltage therebetween; and at least one exploding bridge wire means connected between said sleeve means and said interior portion of said second lead, said exploding bridge wire means in ignition relationship to said secondary explosive powder train, and adapted to explode upon subjection to an electric current at said preselected voltage.

2. In combination: a generally cup shaped case means; a secondary explosive powder train contained within said case means; a dielectric sealing means hermetically sealing said secondary explosive powder train in said case means; a first and a second electrically conductive lead extending through said dielectric sealing means and each of said leads having an interior portion inside said case means and each of said leads electrically insulated from each other and from said case means, said interior portion of said first electrically conductive lead having walls defining a cavity; an electrically conductive pin means contained within said cavity in voltage breakdown gap relationship to said interior portion of said first lead and electrically insulated from said first lead, and defining a voltage breakdown gap therewith for breaking down at a preselected voltage to transmit an electric current at said preselected voltage therebetween; and at least one exploding bridge wire means connected between said pin means and said interior portion of said second lead, said exploding bridge wire means in ignition relationship to said secondary explosive powder train, and adapted to explode upon subjection to an electric current at said preselected voltage.

3. In combination: a generally cup shaped case means; a secondary explosive grain contained within said case means comprised of less than 40 mesh PETN consolidated at 15,000 pounds per square inch; a secondary explosive powder contained within said case means in ignition relationship to said grain and comprised of less than 100 mesh PETN; a polyethylene sealing means hermetically sealing said secondary explosive grain and said secondary explosive powder in said case means; a pair of number 22, American Wire Gage, quadruple Formvar coated, copper wire leads extending through said polyethylene sealing means electrically insulated from each other and from said case means, and each of said leads having an interior portion inside said case means and at least a section of said interior portion of a first of said pair of leads free of said Formvar coating; a secton of Kovar tubing having an outside diameter of 0.040 inch and an inside diameter of 0.030 inch inserted over said interior portion of said first of said pair of leads; dielectric spacer means for electrically insulating said Kovar tubing from said first lead whereby a radial voltage breakdown gap between said section of said interior portion of said first lead and said Kovar tubing of approximately 0.0023 inch is maintained; and a pair of 2 mil gold exploding bridge wires connected in parallel between said Kovar tubing and said interior portion of said second of said pair of leads, said exploding bridge wires in ignition relationship to said secondary explosive powder.

4. A squib initiation circuit comprising, in combination: a pair of number 22, American Wire Gage, quadruple Formv-ar coated, copper wire leads, a first of said pair of leads having a portion substantially free of said Formvar coating and said pair of leads electrically insulated from each other; a section of Kovar tubing having an outside diameter of 0.040 inch and an inside diameter of 0.030 inch inserted over said portion of said first of said pair of leads; a dielectric spacer means for electrically insulating said Kovar tubing from said first lead whereby a radial voltage breakdown gap between said Kovar tubing and said portion of said first of said pair of leads of approximately 0.0023 inch is maintained; and a pair of 2 mil gold exploding bridge wires connected in parallel between said Kovar tubing and said second of said air of leads.

5. A squib initiation circuit contained within a squib comprising, in combination:

a pair of electrically conductive leads;

means defining a voltage breakdown gap comprising a first and a second electric conductor, said first electric conductor comprising an electrically conductive rodlike member and said second electric conductor comprising an electrically conductive sleeve member surrounding at least a portion of said rodlike member;

and a dielectric means between said first and said second electric conductors for electrically insulating said first conductor from said second conductor at voltages less than at preselected voltage and for breaking down at said preselected voltage to transmit an electric current between said first and said second electric conductors;

and said first electric conductor coupled to a first of said pair of electrically conductive leads;

and at least one exploding bridge wire coupled between said second electric conductor and the other of said pair of electrically conductive leads, said at least one exploding bridge wire for exploding upon subjection to an electric current at a voltage other than a voltage less than said preselected voltage.

6. A squib initiation circuit contained within a squib comprising, in combination:

a pair of electrically conductive leads;

means defining a voltage breakdown gap comprising a first and a second electric conductor and said first electric conductor comprising a tube member having walls defining a cavity and said second electric conductor comprising a pin member having at least a portion thereof positioned within said cavity of said first electric conductor, and a dielectric means between said first and said second electric conductors W for electrically insulating said first conductor from said second conductor at voltages less than at preselected voltage and for breaking down at said preselected voltage to transmit an electric current between said first and said second electric conductors;

and at least one exploding bridge wire coupled between said sec-0nd electric conductor and the other of said pair of electrically conductive leads, said at least one exploding bridge wire for exploding upon subjection to an electric current at a voltage less than said reselected voltage.

References Cited by the Examiner UNITED STATES PATENTS 1,333,731 3/20 Ransomer 313-131 X 2,129,003 9/38 Grant 313-139 X 2,189,741 2/40 Minton 102-28 X 2,297,006 9/42 Lohman 102-702 X 2,708,877 5/55 Smits 102-702 2,926,566 3/ Atkins et a1 102-702 2,981,186 4/61 Stresau 102-28 2,996,007 8/61 Franklin 102-28 3,002,458 10/61 Haas 102-702 3,040,660 6/62 Johnston 102-702 X 3,052,185 9/62 Apstein 102-28 3,062,574 11/62 Buntenbach et al 108-28 X SAMUEL FEINBERG, Primary Examiner.

Claims

1. IN COMBINATION: A GENERALLY CUP SHAPED CASE MEANS; A SECONDARY EXPLOSIVE POWDER TRAIN CONTAINED WITHIN SAID CASE MEANS; A DIELECTRIC SEALING MEANS HERMETICALLY SEALING SAID SECONDARY EXPLOSIVE POWDER TRAIN IN SAID CASE MEANS; A FIRST AND A SECOND ELECTRICALLY CONDUCTIVE LEAD EXTENDING THROUGH SAID DIELECTRIC SEALING MEANS AND EACH OF SAID LEADS HAVING AN INTERIOR PORTION INSIDE SAID CASE MEANS AND EACH OF SAID LEADS ELECTRICALLY INSULATED FROM EACH OTHER AND FROM SAID MEANS; AN ELECTRICALLY CONDUCTIVE SLEEVE MEANS IN VOLTAGE BREAKDOWN GAP RELATIONSHIP TO SAID INTERIOR PORTION OF SAID FIRST LEAD AND SAID SLEEVE MEANS ELECTRICALLY INSULATED FROM SAID FIRST LEAD, AND DEFINING A VOLTAGE BREAKDOWN GAP THEREWITH FOR BREAKING DOWN AT A PRESELECTED VOLATAGE TO TRANSMIT AN ELECTRIC CURRENT OF SAID PRESELECTED VOLTAGE THEREBETWEEN; AND AT LEAST ONE XPLODING BRIDGE WIRE MEANS CONNECTED BETWEEN SAID SLEEVE MEANS AND SAID INTERIOR PORTION OF SAID SECOND LEAD, SAID EXPLODING BRIDGE WIRE MEANS IN IGNITION RELATIONSHIP TO SAID SECONDARY EXPLOSIVE POWDER TRAIN, AND ADAPTED TO EXPLODE UPON SUBJECTION TO AN ELECTRIC CURRENT AT SAID PRESELECTED VOLTAGE.