US3557699A

US3557699A - Electroexplosive primer ignition assembly

Info

Publication number: US3557699A
Application number: US740298A
Authority: US
Inventors: Charles L Hubbard
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1968-06-26
Filing date: 1968-06-26
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26

Abstract

An electrically actuated primer ignition assembly displaying a 0.75 ampere ''''no fire'''' characteristic for 60 seconds, and a 2.5 amperes ''''all fire'''' within 10 milliseconds after initial application of current, the ''''all fire'''' performance being maintained even after the ''''no fire'''' preconditionaining.

Description

United States Patent 72] Inventor Cha Hubbard 3,062,146 11/1962 Williams et al. 102 46 Madisflllylll- 3,196,041 7/1965 McNulty et al. 102/28 [21] AppLNo. 740,298 3,227,083 l/1966 Moseset al. 102/28 [22] Filed June 26,1968 3,291,046 12/1966 Dahl 102/28 [45] Patent d Jan. 26, 1971 3,450,045 6/1969 Zedalis 102/28 [73] Asslgnee Olm Comm-anon Primary Examiner verlin R. Pendegrass a corporation 0 Attorneys-Donald R. Motsko, H. Samuel Kieser, William W.

' Jones, Richard S. Strickler, Robert H. Bachman and 54 ELECTROEXPLOSIVE PRIMER IGNITION Thomas y ASSEMBLY 13 Claims, 2 Drawing Figs.

[52] U.S.Cl 102/28 51 Int. Cl F42b3/l2 Field ABSTRACT: An electrically actuated primer ignition as- 149/2143 45 sembly displaying a 0.75 ampere no fire characteristic for References C ed 60 seconds, and a 2.5 amperes all fire within 10 milliseconds after initial application of current, the all fire per- UNITED STATES PATENTS formance being maintained even after the no fire precondi- 3,019,732 2/1962 Kaspaul 102/28 tioning.

PATENTEUJANZGISTI 3557.699

INVENTOR CHARLES L. HUBBARD ATTORNEY ELECTROEXPLOSIVE PRIMER IGNITION ASSEMBLY This invention relates to an electrically actuated primer assembly for use with an ejection-type cartridge of, for example, the Storz variety. The primer assembly of this invention exhibits a no fire characteristic when subjected to a current of a least 0.75 amperes for a period of at least 60 seconds, and further exhibits an all fire characteristic when subjected to a current of only 2.5 amperes which occurs within a period of less than milliseconds. The term no fire, as used in this disclosure, means that no ignition of the primer occurs, and the term "all fire," as used in this disclosure, means that substantially all of the primer is ignited.

It is known in the prior art to provide a cartridge in which a propellant charge is disposed, which propellant charge is utilized to perform some work function. Such cartridges are found, for example, in military aircraft and are used to eject the pilot from a crippled plane. Cartridges of this type are generally ignited by a separate primer charge which is associated with the propellant charge. Electrical ignition assemblies are commonly provided for use in conjunction with the primer charge, so that the primer charge is electrically ignited to fire the cartridge.

It is readily apparent that assemblies of this type are often one shot affairs which may never be used, but which must be ready for use at all times since a man's life may dependon their reliability. It is thus imperative that such assemblies be made susceptible to periodic quality control testing in order to determine their operativeness under all conditions. Ideally, the testing should be capable of being carried out without requiring dismantling of the assembly. Furthermore, the assembly should be capable of being quickly tested under even the most adverse of conditions. One of the most difficult portions of the assembly to testis the electrical circuitry. Ideally, the circuits should be tested by passing an electric current through them, however, since the primer is electrically ignited, one faces the possibility of accidentally igniting the cartridge when thus testing the circuits. Furthermore, in order to reliably test the circuits, a current sufficient to be unaffected by circuit resistance, limits in testing apparatus sensitivity, and the like, must be passed through the circuit. This minimum current has, in the past, been often sufficient to ignite the cartridge during testing. lt would be possible to lower the resistance in the circuit to such a degree that a minimum current passing therethrough would not be capable of accidentally igniting the cartridge, but such a step would then adversely affect the firing capabilities of the assembly. Assemblies of this type must ideally be capable of utilizing a comparatively small current to produce an all fire of the primer within a comparatively brief time period. In order to meet the latter requirement, the resistance of the ignition circuitry should be relatively high.

While in operation, all electrical circuits contained in an aircraft have a continual flow of current, which flow has been termed stray current." The magnitude of stray current can be as high as 0.3 to 0.5 amperes, and thus can present accidental ignition problems with respect to electrical ignition assemblies of the character described.

From the foregoing, it is apparent that an ideal ignition assembly should be capable of being subjected to a comparatively large amperage without igniting, and also should be capable of complete ignition upon the application of a comparatively small amperage. This invention is directed toward an ignition assembly for use with an ejection-type cartridge, which igni-.

tion assembly is electrically actuated. The ignition assembly of this invention can be subjected to a current of at least 0.75 ampere for a period of at least 60 seconds without firing. The application of this current can thus safely be used to test the circuitry in the ignition assembly. The ignition assembly of this invention, furthermore, will fire in a period of less than about 10 milliseconds when subjected to a current of 2.5 amperes or more. lt is thus readily apparent that the ignition assembly of this invention exhibits superior no fire testing characteristics along with excellent all fire characteristics;

Broadly, the ignition assembly of this invention includes: an electrode through which current is fed into the assembly; a ground; means interconnecting the electrode and ground, such as a bridge wire; a heat sink of electrical insulating material contacting the interconnecting means; and, when loaded, a charge of primer material adjacent to the interconnecting means and in intimate contact therewith.

More particularly, the ignition assembly of this invention may include an electrically conducting housing member which is electrically grounded and which has a lining of electrical insulating material. An electrode is disposed in the housing and separated therefrom by the insulating liner. A ground member is disposed in the housing and electrically connected thereto, the ground defining a wall of a chamber into which the primer material is packed. A bridge wire is electrically connected to the electrode and to the ground, the bridge wire extending across the bottom of the primer chamber so as to be in contact with the priming charge when the latter is packed into the chamber. The bridge wire is made of a metal which increases its resistivity as its temperature is increased, thereby providing the heat necessary to ignite the primer charge. A heat sink is disposed in the housing. The heat sink defines the bottom wall of the primer chamber and is in heat exchange contact with the bridge wire. The heat sink underlies the bridge wire and is operative to absorb and conduct heat away from the bridge wire. The heat sink thus contributes to the no fire" charac teristic of the ignition assembly when circuit-testing amperage is applied thereto.

It is, therefore, an object of this invention to provide an electrically operated primer-ignition assembly of compact construction for use with ejection-type cartridges and the like.

It is a further object of this invention to provide an ignition assembly of the character described which will not fire when energized with a current of at least 0.75 amperes for a time period of at least 60 seconds.

It is yet another object of this invention to provide an ignition assembly of the character described which-will completely fire in a time period of not more than about 10 milliseconds when energized with a current of about 2.5 amperes.

vIt is a still further object of this invention to provide an ignition assembly of the character described which will retain its all fire characteristic even after exposure to the no fire condition.

Other features, objects, and advantages of this invention will become apparent to those skilled in the art from the following description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded view of a preferred embodiment of an ignition assembly formed in accordance with this invention; and

FIG. 2 is a side sectional view of the assembly of FIG. 1

Referring now to FIG. 1, the ignition assembly of this invention preferably includes a cup-shaped metallic housing member 2 which is electrically grounded and in which is disposed a lining 4 of electrical insulating material. An electrode 6 is mounted in the liner 4, the electrode 6 preferably including an elongated stem portion 8 for connection with a source (not shown) of electrical current, and an enlarged head portion 10 A post 12 is disposed on the head portion 10, the post 12 projecting through an aperture 14 in a heat sink body 16 adjacent to the electrode head 10. An annular body 18 is mounted in the housing 2 in electrical contact therewith, the body 18 being composed of an electrically conducting material. A bridge wire 20 is disposed between the body 18 and the electrode post 12 to electrically interconnect the latter two. The bridge wire 20 is preferably welded to the body 18 and to the electrode post 12. Furthermore, the bridge wire 20 is disposed in contact 'with the heat sink 16 along substantially the entire length of the bridge wire. Thus, an electrical circuit is established between the electrode 6, the bridge wire 20, the annular body 18, and the housing 2, the latter of which is electrically grounded. i

FIG. 2 shows the assembled ignition assembly, and it is noted that the inner wall of the annular element or ground 18 forms the sidewall of a primer chamber 22. The heat sink 16 forms the bottom wall of the primer chamber 22 and the bridge wire 20 extends across the bottom wall. A charge of primer material 24 is packed into the primer chamber 22. For firing or testing, the electrode stem 8 is connected to a power source (not shown), the housing 2 is grounded, and the primer charge 24 is positioned next to a body of propellant (not shown) to be ignited by the assembly.

With reference now to the specifics of the ignition assembly of this invention, the bridge wire is preferably formed from Nichrome alloy, with the physical embodiment of the bridge wire being controlled so as to provide a total unit resistance in the range of about 1.2-2.0 ohms. While Nichrome is the preferred bridge wire material, other materials having a temperature coefficient of resistivity approximately equal to about .0004 ohm-cm. at 20 C. could be used in place of Nichrome.

The heat sink is preferably formed from Alumina. The heat sink may also be formed from a precast machined body of thermosetting epoxy resin, or from a mineral filled thermosetting epoxy resin, or from a potted thermosetting epoxy resin. The heat sink must be formed from an electrical nonconductor and should have a thermal conductivity in the range of about .002 to .040*. The heat sink should also have an adequate temperature stability at about 300 C. for time durations of 60 seconds to prevent excessive melt.

The primer composition is formed from a homogeneous mixture of about 18 percent to about 30 percent powdered zirconium, about 14 percent to about 26 percent antimony sulfide, and from about 5 percent to about 70 percent barium nitrate. The primer mixture is preferably granulated to pass through a 325 mesh and is compacted into the primer chamber with a compaction pressure of greater than 6,000 psi. The preferred range of compaction pressures is from 8,000-l2,000 p.s.i. While the preferred granulation of the primer mixture is such as will pass through a'325-mesh screen, one may use a more coarsely granulated mixture without departing from the spirit of this invention. The coarsening of the primer will not adversely affect the no fire and all fire characteristics of the assembly of this invention, but will merely vary the burning properties of the primer.

Several variations of the ignition assembly of this invention were tested for no fire and all fire characteristics, using different ram calories centimeter thickness Units of (centiilieter) seconds degrees 0 heat sink materials. The tested assemblies all had bridge wires of Nichrome with a unit resistance in the 1.2 ohm to 2.0 ohm range, and were packed with a preferred primer composition of 24 percent powdered zirconium, 20 percent antimony sulfide, and 56 percent barium nitrate. Table 1 shows the no fire results of the tests, and table [I s h ows t h e all fire results.

TABLE I Current amps; 100% no fire Heat sink composition 60 seconds No. Tested:

50 Epoxy 0. 8 Mineral filled epoxy 1. 0 50 Alumina 1.2

TABLE II Average firing time, Current, milli- Heat sink composition amps seconds No. Tested:

20 Epoxy 3.0 2.15 20. Mineral filled epoxy. 2 5 4. 22 20 Alumina 2. 5 5. 09

it is thus readily apparent that the ignition assembly of this invention is capable of being easily tested for operativeness by the passage of a comparatively high current therethrough without an attendant combustion of the primer charge. At the same time. however, the ignition assembly of this invention produces complete combustion of the primer charge in a comparatively brief time upon the application thereto of a comparatively low current. Furthermore, the excellent all fire characteristics of the ignition assembly of this invention are not affected by a prior application of the no fire current for testing.

It is to be understood that various modifications and alterations will readily suggest themselves to persons skilled in in the art. It is intended, therefore, that the foregoing description be considered as exemplary only, and that the scope of this invention be defined by the following claims.

lclaim:

1. An electrical ignition assembly for firing an adjacent mass of propellant, said assembly, when loaded, exhibiting a no-fire characteristic of at least 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most 10 milliseconds when subjected to a current of at least 2.5 amperes, said ignition assembly comprising:

a. an electrode;

b. electrically insulating heat sink means having a thermal conductivity in the range of about 002 gm.2cal. to about .040 gm. cal. ate-"se nsec}- Q-..

o. a bridge wire connected to said electrode, said bridge wire being disposed in heat exchange relationship with said heat sink means, said bridge wire having a temperature coefficient of resistivity of approximately .0004 ohmcm at 20 C., and a unit resistance in the range of about 1.2. ohms to about 2.0 ohms; and

d. electrical ground means connected to said bridge wire.

2. The ignition assembly of claim 1, further comprising a charge of a densely packed homogenous mixture of granulated primer material disposed adjacent to said bridge wire, said primer material consisting essentially of about 18 percent to about 30 percent powdered zirconium, about 14 percent to about 26 percent antimony sulfide, and about 50 percent to about percent barium nitrate. v

3. The ignition assembly of claim 2, wherein said heat sink means is formed from a material selected from the group consisting of thermosetting epoxy resin, thermosetting mineralfilled epoxy resin, and alumina.

4. The ignition assembly of claim 2, wherein said bridge wire is Nichrome.

5. The ignition assembly of claim 2, wherein said granulated charge of primer material is of a particle size which will pass through a 325-mesh screen.

6. The ignition assembly of claim 2, wherein said primer material contains about 24 percent powdered zirconium, about 20 percent antimony sulfide, and about 56 percent barium nitrate.

7. An electrical ignition assembly for firing an ejection type cartridge, said assembly exhibiting a no-fire characteristic of at least 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most 10 milliseconds when subjected to a current of at least 2.5 amperes, said ignition assembly comprising:

a. an electrode for connection to a source of electric current;

b. electrically grounded means defining a sidewall of a primer chamber;

c. an electrically insulating heat sink body interposed between said electrode and said grounded means, said heat sink body defining a bottom wall of said primer chamber and said heat sink body being formed from a material selected from the group consisting of thermosetting epoxy resin, thermosetting mineral-filled epoxy resin, and alumina; and

d. a bridge wire interconnecting said electrode and said grounded means, said bridge wire extending across the bottom wall of said primer chamber in face-to-face contact with said heat sink body, said bridge wire having a temperature coefficient of resistivity of approximately .0004 ohm-cm at 20 C. and a unit resistance in the range of about 1.2 ohms to about 2.0 ohms.

8. The ignition assembly of claim'7, further comprising a granulated homogeneous mixture of primer material densely packed into said primer chamber to contact said bridge wire, said primer material consisting essentially of from about 18 percent to about 30 percent powdered zirconium, from about 14 percent to about 26 percent antimony sulfide, and from about 50 percent to about 70 percent barium nitrate.

9. The ignition assembly of claim 7, wherein said bridge wire is Nichrome.

10. The ignition assembly of claim 8, wherein said granulated charge of primer material is of a particular size which will pass through a 325-mesh screen.

11. The ignition assembly of claim 8, wherein said primer material contains about 24 percent powdered zirconium, about 20 percent antimony sulfide, and about 56 percent barium nitrate.

12. An electrical ignition assembly for firing an ejectiontype cartridge, said assembly, when loaded, exhibiting a nofire characteristic of at least 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most about milliseconds when subjected to a current of at least about 2.5 amperes, said ignition assembly com prising:

a. a housing of electrical conducting material for connection to an electrical ground;

b. a lining of electrical insulating material disposed in said housing;

c. an electrode disposed in said housing and separated therefrom by said lining, said electrode being for connection to a source of electric current;

d. an electrically Calif. element disposed in said housing and electrically connected thereto, said element defining a wall of a primer chamber;

e. an electrically insulating heat sink body interposed between said electrode and said element, said heat sink body defining a bottom wall of said primer chamber and said heat sink body being formed from a material selected from the group consisting of thermosetting epoxy resin, mineral filled therrnosetting epoxy resin, and alumina; and

f. a Nichrome bridge wire interconnecting said electrode and said element, said bridge wire extending across the bottom wall of saidprimer chamber in contact with said heat sink body, and said bridge wire having a unit resistance in the range of about 1.2 ohms to about 2.0 ohms.

13. An electrical ignition assembly for firing an ejectiontype cartridge, said assembly comprising:

a. an electrode for connection to a source of electric current;

b. an element for connection to an electrical ground, said UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,557 ,699 January 26, 1971 Patent No. Dated Charles L. Hubbard Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6 claim 12 line 6 "Calif." should read conducting Signed and sealed this 1st day of June 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69 nernnnhnr nae-IA

Claims

1. An electrical ignition assembly for firing an adjacent mass of propellant, said assembly, when loaded, exhibiting a no-fire characteristic of at least 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most 10 milliseconds when subjected to a current of at least 2.5 amperes, said ignition assembly comprising: a. an electrode; b. electrically insulating heat sink means having a thermal conductivity in the range of about

2. The ignition assembly of claim 1, further comprising a charge of a densely packed homogenous mixture of granulated primer material disposed adjacent to said bridge wire, said primer material consisting essentially of about 18 percent to about 30 percent powdered zirconium, about 14 percent to about 26 percent antimony sulfide, and about 50 percent to about 70 percent barium nitrate.

3. The ignition assembly of claim 2, wherein said heat sink means is formed from a material selected from the group consisting of thermosetting epoxy resin, thermosetting mineral-filled epoxy resin, and alumina.

4. The ignition assembly of claim 2, wherein said bridge wire is Nichrome.

7. An electrical ignition assembly for firing an ejection type cartridge, said assembly exhibiting a no-fire characteristic of at leasT 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most 10 milliseconds when subjected to a current of at least 2.5 amperes, said ignition assembly comprising: a. an electrode for connection to a source of electric current; b. electrically grounded means defining a sidewall of a primer chamber; c. an electrically insulating heat sink body interposed between said electrode and said grounded means, said heat sink body defining a bottom wall of said primer chamber and said heat sink body being formed from a material selected from the group consisting of thermosetting epoxy resin, thermosetting mineral-filled epoxy resin, and alumina; and d. a bridge wire interconnecting said electrode and said grounded means, said bridge wire extending across the bottom wall of said primer chamber in face-to-face contact with said heat sink body, said bridge wire having a temperature coefficient of resistivity of approximately .0004 ohm-cm at 20* C. and a unit resistance in the range of about 1.2 ohms to about 2.0 ohms.

8. The ignition assembly of claim 7, further comprising a granulated homogeneous mixture of primer material densely packed into said primer chamber to contact said bridge wire, said primer material consisting essentially of from about 18 percent to about 30 percent powdered zirconium, from about 14 percent to about 26 percent antimony sulfide, and from about 50 percent to about 70 percent barium nitrate.

9. The ignition assembly of claim 7, wherein said bridge wire is Nichrome.

12. An electrical ignition assembly for firing an ejection-type cartridge, said assembly, when loaded, exhibiting a no-fire characteristic of at least 60 seconds duration when subjected to a current of approximately 0.75 ampere, and said assembly further exhibiting an all-fire characteristic occurring within at most about 10 milliseconds when subjected to a current of at least about 2.5 amperes, said ignition assembly comprising: a. a housing of electrical conducting material for connection to an electrical ground; b. a lining of electrical insulating material disposed in said housing; c. an electrode disposed in said housing and separated therefrom by said lining, said electrode being for connection to a source of electric current; d. an electrically Calif. element disposed in said housing and electrically connected thereto, said element defining a wall of a primer chamber; e. an electrically insulating heat sink body interposed between said electrode and said element, said heat sink body defining a bottom wall of said primer chamber and said heat sink body being formed from a material selected from the group consisting of thermosetting epoxy resin, mineral filled thermosetting epoxy resin, and alumina; and f. a Nichrome bridge wire interconnecting said electrode and said element, said bridge wire extending across the bottom wall of said primer chamber in contact with said heat sink body, and said bridge wire having a unit resistance in the range of about 1.2 ohms to about 2.0 ohms.

13. An electrical ignition assembly for firing an ejection-type cartridge, said assembly comprising: a. an electrode for connection to a source of electric current; b. an element for connection to an electrical ground, said element defining a sidewall of a primer chamber; c. an electrical insulating heat sink body interposed between said electrodE and said element, said heat sink body defining a bottom wall of said primer chamber; and d. a bridge wire interconnecting said electrode and said element, said bridge wire extending across the bottom wall of said primer chamber in heat exchange contact with said heat sink body.