US3118375A

US3118375A - High-tension or spark-type electric igniter

Info

Publication number: US3118375A
Authority: US
Priority date: 1959-05-04
Publication date: 1964-01-21
Anticipated expiration: 1981-01-21
Also published as: FR1233618A; DE1132475B; CH361221A; GB885964A; BE589706A; NL251162A; ES257791A1; NL110257C

Description

Jan. 21, 1964 J. R. JAssE HIGH-TENSION OR SPARK-TYPE ELECTRIC IGNITER Filed April 2'?, 1960 l 2 m 7 n /////////////////////////////Yr///V7/456.

United States Patent C HIGHJENSEUN @R SPARKWTYPSE ELECTRC llGNlllllR Joseph Raymond lasse, Paris, France, assignor to Hotell kissllrandt, Paris, France, a French body corporate Filed Apr. 27, woll, Ser. No. 25,946 @Claims priority, application France May 4, 1959 8 Claims. (Cl. to2-Z8) The present invention relates to electric igniters of the so-oalled high-tension or spark-type, usable for the igniting of an explosive charge, more particularly in mines, clearing work and for missiles.

'l` his type of igniter comprises, as is known, two electrodes connected with a source of electric current and separated by a dielectric.

Various embodiments of this type or igniter are known in the art. For high-voltage operating, the dielectric employed is an electrically non-conductive explosive. The explosive is fused by the spark generated between the two electrodes, but such an igniter requires a powerful electric generator, capable of producing a voltage of eg. 29,610@ volts, whereby the igniter can only be used in practice for mine-blasting and clearing work.

ln order to enable such an igniter to be used as a missile in which the generator, owing to the available-space limitation, has to be compulsorily operated under a much more reduced terminal voltage, the dielectric has imparted thereto a certain amount o conductibility by adding thereto iinely divided graphite or powdered metals. The interspace between the two electrodes, filled with this mixture, provides a suc ession of small slits or cracks, by virtue of which the explosive mixture of the so-called slotted type permits the `formation of a spark under a lower voltage, say of about l) volts. But:

Gn the one hand, the formulation of the explosive mix.- ture and of powdered metals used as an electric resistance between the two electrodes is highly critical, since the conducting properties have to be accurately delined in relation to the available electric voltage; and

On the other hand, since it is only possible to house within a missile or a projectile a small type of generator, the ignitcr has to be charged with a very sensitive fusing explosive, thus considerably compromising the safety factor of the missile provided with such an iguiter.

The object of the present invention is to overcome the aforesaid drawbacks, by the provision of an improved spark-type electric igniter, easy to manufacture with the help of very simple means and endowed with electrical properties of a readily reproducible type, this being a highly advantageous feature when such igniters are to be produced on a large industrial scale.

I-finis improved spark-type electric igniter is of the kind embodying two electrodes separated by a dielectric layer; it is essentially characterised in that one of the electrodes is comprised of an electrically conducting explosive.

According to one embodiment, the dielectric layer consists of an insulating member having at the location where the spark is due to occur, a hole of a lower crosssectional area than the grain size of the conducting explosive.

According to a further embodiment, the dielectric layer is formed of a layer ot a crystalline semi-conducting material, such as the oxide or the carbide of the metal of which the second electrode or electrode not made ot the oresaid explosive material, is -orme l.

rhis crystalline semi-conducting material enables the current to pass from one electrode to the other through one or a plurality of electron-emitting points, this being a well-known discharge phenomenon which occurs always in the orm of sparks if the disruptive voltage is reached.

rthe conductioility of the explosive used as electrode Cil can be achieved by any one of the known methods, for instance by mixing the explosive with a conducting agent such as lgraphite or powdered metal.. Whereas the proportions of the mixture are highly-critical when it is desired to provide, as in the case with certain of the known igniters, a layer having a \voll-delincd electrical resistance with such a mixture, this is not so in the case of an electrode formed with a conducting explosive, wherein the proportions in the mixture can l'luctuate between comparatively wide limits, the included percentage of the conducting agent being for example comprised between l() and Z0 by weight, without any eleterious elect of the operation of the igniter.

Further features of this invention will become apparent `from the ensuing description, when read in connection with the accompanying drawing, given merely by way of an example and in which:

PIG. l is a diagrammatical sectional elevation of an improved ignitcr designed in accordance with the invention;

FGS. 2 to 5 are s' jiilar sectional elevation views of other embodiments of the invention.

Referring first to the embodiment illustrated in FIG. l of the patent drawing, an igniter A1 comprises a metal cap or hollow body l having a hole 2 formed in the bottorn portion thereof to provide for the centre-ring of an insulating ring 3 of a plastic, ceramic or like material. This insulating ring 3 provides a supporting means of a first electrode l formed of a metal.

This electrode is lapped with a dielectric layer 5 con sisting of a thin disc, preferably formed of a plastic, but whi n may alternatively be formed of paper or another material. This disc has centrally formed therein a very narrow hole or perforation 6 having a diameter of about 0.01 mm. and providing a very short channel through which the fusing electric spark is due to pass. This perforation or channel 6 can be advantageously formed by perforating plate by means of a high-voltage spark, this operation being of course ellected prior to the disc being posi 'cned in the igniter.

Above this disc is located a second electrode 7 consisting ci a layer ot fusing explosive, which has been made conducting, as earlier mentioned, by a mixture with a conducting agent such as graphite or powdered metal. The explosive may advantageously be comprised by lead nitride or trinitroresorcinate or a mixture thereof, and when a metal powder is being employed it may be powdered aluminium, copper etc. This only requirement is that the used powder should not be chemically attackable by the actual explosive.

Overlying the second electrode '7, a non-conducting fusing explosive S may consist lor example of lead nitride, this material being overlaid in turn by a secondary explosive charge '9, which can be comprised by tetryl, penthrite, hexogen, tolite or the like.

All the elements enclosed in the cap l forming the igniting unit are held, for example by inserting at l0, at a distance from the end of the cap.

By energising the cap l and the electrode 4 under a voltage U, for example through contact members `la and da, the electrodes Il and 7 located either side of the dielectric 5 are energized with the same voltage and a spark is generated therebetween which passes through the perforation lor channel 6, provided centrally in the insulating disc 5, thus causing the electrode formed of the conducting explosive 7 to be detonated. This electrode in turn fuses the non-conducting explosive il, which tires the secondary explosive charge i?.

ln FlG. 2 there is shown an igniter A2 whose electrode l is surface-coated with a dielectric layer 5o and covered with an insulating disc ll, having a central hole l2 bored therethrough. lt is through this hole that the explosive conductor '7 which plays the part of the second electrode comes into contact with the dielectric layer 5a.

In this case, the electric discharge takes place through said dielectric layer 5a to generate a spark at the spot at which the electric resistance is the lower, i.e. at the ocation between both

electrodes

4 and 7 having no insulating disc 11 interposed therebetween, i.e. at right angles to the hole 12 formed in said disc.

The electrode 4 can be formed e.g. of aluminium, the dielectric layer 5a being formed of an oxide coating obtained by anodic oxidation. Such an oxide layer does not afford a genuine crystalline structure, but it has actually very small-sectioned channels extending therethrough leaving for the current a passage of predetermined cross-sectional area.

Such an anodic layer may be formed by simple means for disruptive voltages of from 50 to 300 volts.

For lower voltages, for example in the range of 20-50 volts, it is possible to use an aluminium electrode 4 which is chemically surface-coated with a layer of oxide 5a. This oxide layer has a specific crystalline structure and the passage of the current is afforded for a small disruptive voltage through emitting centres, as is well-known in the art of semi-conductors. The discharge takes place notwithstanding the low voltage and is accompanied by a spark generation. If it is desired to use the same very simple means to obtain high disruptive voltages, it is sucient to impregnate the layer formed by the chemical oxidation with an insulating varnish. The oxide layer can be replaced, if desired, by a carbide coating.

Such semi-conducting oxide layers can also be formed chemically, electrolytically or thermally on other metals and alloys, e.g. iron, copper etc.

In FIG. 3 is illustrated a third modification of the igniter according to the invention; the igniter A3 is similar to the preceding embodiment thereof, except that the disc 11 bored centrally with a hole 12 is overlaid by a metal capsule 13 having a central hole 14, adapted to reduce the amount of conducting explosive 7 used as an electrode.

In this instance, the discharge is effected from the electrode 4, through the dielectric layer 5a and to the electrode 7, and the current passes through the capsule 13 to reach the cap 1.

In FIG. 4 is shown a further igniter A4 in which two insulated leads 15 and 16 act as electrodes, the conducting explosive 7 being in this case used as an intermediate electrode. Thus, both leads 15 and 16 are braided on a certain length thereof from their ends, at least one of which is pre-coated with a dielectric layer preferably an oxide coating formed by electrolytical or chemical means. The thus-formed twisted portion is thereafter housed in a plastic body 17, which is in turn pushed home into the bottom of the cap 1. The coated ends of the leads projecting from the front surface 18 of the body 17 are finally ground at the level of this surface, whereby the ground remaining part 5b of the dielectric layer coating at least one end of the lead comes flush, owing to the grinding step, with the surface 1S.

The ground remaining part 5b of the dielectric layer has superposed thereon the explosive 7 which is adapted to constitute an intermediate electrode between the leads 15 and 16, and above this explosive 7, there are disposed, as previously stated, the fusing explosive 8 and finally the second explosive 9.

In this modification, the igniting of the explosive layer 7 is ensured by a spark which is generated between said layer 7 and one of the leads 15 or 16.

This is likewise the case of the gniter A5 shown in FIG. 5 and wherein the ends of the leads 15 and 16, playing the part of electrodes, are flush with the bottom of a recess 19 provided in the insulating support 17. At least one of them is coated, as in the preceding example, with the dielectric layer 5b, having the conducting explo- CII '4 sive layer 7 forming the intermediate electrode disposed thereover.

This sub-assembly 151-175b7 can in this case be independent from the remaining part of the igniter, which may be comprised by a usual type of commerciallyavailable detonator, having an igniting charge 2t) and a main charge 21.

It will be apparent from the foregoing that the main advantage of the invention lies in the possibility of producing, using extremely simple means, a dielectric layer 5, Sfz or part 5b intermediate the electrodes, i.e. between the electrode 4 and the explosive electrode '7 (in the case of FIGS. l, 2, 3) or between each of the leads 15, 16 and the explosive layer 7 (FIGS. 4 and 5), this being effected with a great uniformity by suitably selecting, by way of a simple disruption test, the thickness of the insulating disc 5 or of the dielectric layer 5a or part 5b for a given operational voltage.

The explosive electrode 7 always receives the available electric energy in the form of a spark. As has already been stated, the conductibility of the explosive, which has to be of an accurately defined value in the case of the so-called slotted ignters, in which said explosive acts as an electrical resistance, can on the contrary be varied between comparatively wide limits in the arrangements provided by this invention, without forfeiting the successful operating characteristics of the igniter. This greatly facilitates the production on an industrial scale.

In the so-called slotted igniter, when the conductibility of the explosive is too high, the current passes without sparking, whereas when this conductibility is too low, the current meets with too high a resistance and thus prevents a spark from being generated. The ignter provided by the invention eliminates entirely these drawbacks.

It is to be understood that the invention is in no way limited to the embodiments which have just been described and illustrated, since various modifications can be made therein without falling outside the scope of the appended claims. p Y

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

l. A spark type electric igniter comprising in combination a iirst metal electrode and a second electrode which consists of an electrically conductive explosive material, an insulating element having a throughway aperture, the second electrode abutting the insulating element and having a portion extending through said aperture, a dielectric layer located between and adjoining the insulating element and the first electrode and adjoining said portion of the second electrode extending through said aperture, an explosive charge adjoining the second electrode on the side of the second electrode remote from the insulating element, the electrical characteristics of said conductive explosive material relative to the electrical characteristics of said dielectric layer being such that said conductive explosive material allows the passage therethrough of an electric current sutiicient for generating an electric spark in said dielectric layer between said electrodes without said passage of current directly igniting said conductive explosive material as a result of the Joule effect, and means connected to said electrodes for supplying said current generating said spark and thereby igniting said conductive explosive material.

2. A spark type electric igniter comprising in combination a first metal electrode and a second electrode which consists of an electrically conductive explosive material, an insulating element having a throughway aperture, a metal element having a throughway aperture, and abutting said insulating element, said throughway apertures being in alignment with one another, an explosive charge adjoining the metal element on the side of the metal element remote from the insulating element, a dielectric layer located between and adjoining the insulating element and the first electrode, the second electrode extending through said aligned throughway apertures and having one end adjoining the dielectric and the other end adjoining said explosive charge, the electrical characteristics of said conductive explosive material relative to the electrical characteristics of said dielectric layer being such that said conductive explosive material allows the passage therethrough oi an electric current suicient for generating an electric spark in said dielectric layer between said electrodes without said passage ol current directly igniting Said conductive explosive material as a result of the loule effect, and means connected to said electrodes for supplying said current generating said spark and thereby igniting said conductive explosive material.

3. A spark type electric igniter comprising in combination a hollow metal body having a lower opening and containing, mounted in the body: a metal iirst electrode having a relatively large substantially tlat face, a dielectric 4layer overlying and adjoining said face of the first electrode, a second electrode overlying and adjoining the dielectric layer, an explosive charge overlying and touching the second electrode, the iirst electrode being accessible from outside the body through said opening, means electrically insulating the lirst electrode from the body, the second electrode consisting of an electrically conductive explosive material and in electrical contact with the body, whereby when a source of electricity is connected to the body and the lirst electrode for generating an electric current in the body, the second electrode and the lirst electrode so as to generate an electric spark across the dielectric layer said conductive explosive material is ignited by said spark and causes ignition of said explosive charge, the electrical characteristics of said conductive explosive material relative to those of said dielectric layer being such that it allows the passage of said current therethrough without being directly ignited by said passage of said current as a result of the Joule etlect.

4. An igniter as claimed in claim 3, further comprising an insulating element having a throughway aperture and interposed between the second electrode and the dielectric layer except in said aperture, a portion of the second electrode extending through said aperture and adjoining the dielectric layer.

5. An igniter as claimed in claim 3, further comprising an insulating element having a throughway aperture, a metal member having a throughway aperture, and overlying and adjoining the insulating element, said throughway apertures being in alignment with each other, the insulating element and the metal member being interposed between the dielectric layer and said explosive charge, and the second electrode being disposed in said aligned throughway apertures and in electrical contact with the metal rneinber, said metal member being in electrical contact with the metal body.

6. An igniter as claimed in claim 3, wherein said explosive charge comprises two superimposed layers, one ot said layers being an igniting layer touching the second electrode and the other ot said layers overlying the igniting layer and being a secondary explosive.

7. A spark type electric igniter comprising in combination a hollow metal body having a lower opening and containing, mounted in the body: an insulating block having a transverse face, a iirst insulated electrical conductor and a second insulated conductor partly embedded in the block and issuing from the lower end of the block and from the body by way of said opening, said iirst conductor having an end set back from said face of the block, said second conductor having an end ilush with said face, said lirst conductor constituting a first electrode, a second electrode which consists of an electrically conductive explosive material and overlies and adjoins said face and said second conductor end so that said second conductor end is in electrical contact with the second electrode, a thin dielectric layer disposed between and adjoining said end of the irst conductor and the second electrode, an explosive charge overlying and adjoining the second electrode, whereby when a source of electricity is connected across said conductors for generating an electric current in said conductors and said second electrode which generates an electric spark across the dielectric layer, said conductive explosive material is ignited by said spark and consequently ignites said explosive charge, the electrical characteristics of said conductive explosive material relative to the electrical characteristics of said dielectric layer being such that said conductive explosive material allows the passage of said current without being directly ignited by said passage of said current.

8. An igniter as claimed in claim 7, wherein said block comprises a recess having a bottom constituting said transverse face, the recess being filled by the second electrode.

References Cited in the le of this patent UNlTED STATES PATENTS 319,628 Russell June 9, 1885 2,872,870 Gey Feb. l0, 1959 2,918,871 Taylor Dec. 29, 1959 2,960,032 Sahlin Nov. 15, 1960 2,996,944 Chessin et al. Aug. 22, 1961 3,962,458 Haas Oct. 3, 1961 3,0l9,732 aspaul Feb. 6, 1962

Claims

3. A SPARK TYPE ELECTRIC IGNITER COMPRISING IN COMBINATION A HOLLOW METAL BODY HAVING A LOWER OPENING AND CONTAINING, MOUNTED IN THE BODY: A METAL FIRST ELECTRODE HAVING A RELATIVELY LARGE SUBSTANTIALLY FLAT FACE, A DIELECTRIC LAYER OVERLYING AND ADJOINING SAID FACE OF THE FIRST ELECTRODE, A SECOND ELECTRODE OVERLYING AND ADJOINING THE DIELECTRIC LAYER, AN EXPLOSIVE CHARGE OVERLYING AND TOUCHING THE SECOND ELECTRODE, THE FIRST ELECTRODE BEING ACCESSIBLE FROM OUTSIDE THE BODY THROUGH SAID OPENING, MEANS ELECTRICALLY INSULATING THE FIRST ELECTRODE FROM THE BODY, THE SECOND ELECTRODE CONSISTING OF AN ELECTRICALLY CONDUCTIVE EXPLOSIVE MATERIAL AND IN ELECTRICAL CONTACT WITH THE BODY, WHEREBY WHEN A SOURCE OF ELECTRICITY IS CONNECTED TO THE BODY AND THE FIRST ELECTRODE FOR GENERATING AN ELECTRIC CURRENT IN THE BODY, THE SECOND ELECTRODE AND THE FIRST ELECTRODE SO AS TO GENERATE AN ELECTRIC SPARK ACROSS THE DIELECTRIC LAYER SAID CONDUCTIVE EXPLOSIVE MATERIAL IS IGNITED BY SAID SPARK AND CAUSES IGNITION OF SAID EXPLOSIVE CHARGE, THE ELECTRICAL CHARACTERISTICS OF SAID CONDUCTIVE EXPLOSIVE MATERIAL RELATIVE TO THOSE OF SAID DIELECTRIC LAYER BEING SUCH THAT IT ALLOWS THE PASSAGE OF SAID CURRENT THERETHROUGH WITHOUT BEING DIRECTLY IGNITED BY SAID PASSAGE OF SAID CURRENT AS A RESULT OF THE JOULE EFFECT.