US3295447A

US3295447A - Electric match assembly and electric explosion initiators made therewith

Info

Publication number: US3295447A
Application number: US446797A
Authority: US
Inventors: William D Trevorrow
Original assignee: Atlas Chemical Industries Inc
Current assignee: Zeneca Inc
Priority date: 1965-04-06
Filing date: 1965-04-06
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03

Description

Jan. 3, 1967 Y w. D. TREVORROW 3,295,447 ELECTRIC MATCH ASSEMBLY AND ELECTRIC EXPLOSION INITIATORS MADE THEREWITH Filed April 6. 1965 2 Sheets-Sheet 1 INVENTOR. Will ium D. Trevorrow @wAXQ. SSMUSJY Ji-In- 1967 W D. TREVORROW 3,295,447

ELECTRIC MATCH :ASSEMBLY AND ELECTRIC EXPLOSION INITIATORS MADE THEHEWITH' Filed April 6, 1965 2 Sheets-Sheet 2 FIG. 3 FIG'.4

} INVENTOR. Willlcm D. Trevorrow :ELECTRIC MATCH United States Patent 3,295,447 ASSEMBLY AND ELECTRIC EXPLOSION INITIATORS MADE THEREWITH William D. Trevorrow, Tamaqua, Pa., assignor to Atlas Chemical Industries, Inc., Wilmington, Del., a corporation of Delaware Filed Apr. 6, 1965, Ser. No. 446,797 21 Claims. (Cl. 102-28) This application is a continuation-in-part of application -Ser. No. 368,751, filed May 4, 1964 which in turn is a continuation-impart of application Ser. No. 313,493, filed Oct. 3, 1963, now abandoned.

The present invention relates to an improved electric match assembly which contains an electrical bypass. A portion of the bypass path is through a semi-conductive material. The present invention also relates to an electric explosion initiator which incorporates the present improved match assembly.

The danger of extraneous electrical energy in blasting circuits has long been recognized. The ignition compositions generally used in commercially available initiators arehighly heat sensitive and exposure of the bridge wire to extraneous electricity is quite capable of igniting the ignition composition and subsequently firing the initiator.

Although the danger from accidental firing of detonators by extraneous electricity is present in almost all blasting operations, the danger is particularly present when the blasting operation is carried out under conditions conducive to high levels of either atmospheric static electricity, for example, in electrical, dust or snow storms; or, in operations susceptible to the generation of static charges, for example, operations wherein a particulate blasting agent, such as sensitized ammonium nitrate is blowloaded, e.g., loaded into a bore hole by a stream of compressed air.

A number of solutions to the problem of static susceptibility of electric detonators are known, and most solutions have been effective at least to some degree. However, none have been found to be entirely satisfactory when cost, ease of manufacture, effectiveness, and storage life areall considered.

One means of protecting an electric initiator from premature initiation by extraneous static charges has been by means of a semi-conductive plug positioned within the detonator shell surrounding and in intimate contact with bared portions of the leg Wires and extending to close proximity with the inside shell wall. The plug is spaced from the shell wall by a distance substantially less than the distance between either of the leg wires and the shell Wall in the locus of the ignition composition. Thus, a static charge may be conducted to the edge of the semiconductive plug-body and allowed to discharge to the shell wall. In this manner the static charge may be grounded to the shell outside the locus of the ignition composition.

The term semi-conductive as used herein describes the property of a material to act as an insulator at low voltages, for example, up to 100 volts, but act as a low resistance material when exposed to high voltages comparable to those required to initiate an initiator by a charge of static electricity. A semi-conductive material presents a conductive path for high voltage, static discharges and a high resistance path to a low voltage of the type used normally to fire the initiator.

A typical protective plug of the prior art is a semiconductive body made up of a wax matrix and including a quantity of finely divided conductive material therein. Examples of the finely divided conductive materials generally used are powdered aluminum, carbon, galena, brass or copper. A serious disadvantage of the prior art protective plugs is the difficulty of maintaining intimate con- 3,295,447 Patented Jan. 3, 1967 tact between the leg wires and the protective plug, particularly during the initiator manufacturing process wherein the various component parts are assembled. Generally the greater the quantity of conductive material in a plug, the greater the degree of static protection which is obtained. However, the plugs become more brittle with an increase in content of conductive material. Brittleness causes ruptures or cracks extending along the interface between the leg Wires and the protective plug which reduce the area of intimate contact between the leg wires and the plug. This condition markedly and adversely affects the efliciency of the plug to afford protection against static charges. Prior art plugs are often brittle and susceptible to cracking or splitting when the leg wires therein are subjected to a very slight pull or tug of A to pound. It is most difiicult to assemble an initiator containing a prior art protective plug and not expose the leg wires positioned through the plug to slight tugs suflicient to crack the plug. The present invention provides a means of efliciently positioning a plug of semi-conductive material between the electrical lines to rotect the initiator from extraneous static charges. The present means may be entirely incorporated in a match head of standard dimensions. The present invention also provides intimate support of the semi-conductive plug in all directions which drastically lessens any chance of a crack or split in the plug during assembly and later handling. The present invention also allows the incorporation of a large, up to 99% by weight, amount of conductive material in the semi-conductive plug.

It has also been discovered that various malfunctions of delay electric initiators, which are seemingly unrelated, are caused by a large amount of heat, generated by an electrical are which occurs within the initiator when an excessive electrical current is supplied. The gases from the ignition composition within the initiator are heated rapidly and a high internal pressure is soon built up. The heat and high pressure condition within the initiator causes either an outward rupture of the initiator Wall or a violent dislodging of the initiator seal, and the enclosed hot gases are rapidly released. The eifect of this action on the blasting operation is unpredictable and varied. The sudden release of the gases may create conditions under which the burning delay element may be' extinguished or the speed of burning of the delay element is retarded. The delay element will then fail to initiate the explosive charge of the initiator at the precise time interval. The release of the hot gases and flame can ignite the surrounding explosive which may slowly burn with the possibility of detonation developing. If the delay element is extinguished and the surrounding explosive charge is ignited, several minutes may elapse before heat from the burning explosive either causes detonation or ignites the explosive charge of the initiator which initiates the remainder of the burning explosive. Heat generated by the burning explosive may decompose the explosive charge of the initiator, and, in such case, the surrounding explosive may, unpredictably, either burn completely or detonate at any point before it is completely consumed by burning. If the burning element is extinguished by the sudden release of the entrapped gases, and the explosive charge is not ignited by the hot gases, the shot may fail completely. Thus, the occurrence of a violent electrical are within the delay electric initiator may result in various malfunctions such as: a premature detonation, a misfire, or a delayed voltage across the bridge wire terminals frequently is high enough to sustain an electrical arc after the bridge wire melts, and, when a power line of high current capacity is used, the arc may generate enough heat within the initiator prior to initiation to cause malfunction. Parallel circuit arrangements of delay initiators are often used in the blasting art and the convenience and advantages of a power line as a source of electrical energy are well-known. Thus, the majority of arcing difiiculties encountered in blasting operations occur when a commonly used circuit arrangement is combined with a commonly used source of electrical energy.

In accord with the present invention a match assembly is provided which includes an electrical bypass. A portion of the bypass path is through a semi-conductive material. The present match assemblies comprise a pair of conductive tabs which have a bottom portion and a portion broader than said bottom portion. The tabs are seperated by a layer of nonconductive material and have a connecting bridge wire along their bottom portions. An ignition composition is positioned in ignitable relation to the bridge wire; The tabs of the present match are in close electrical contact with a plug of semioonductive material which connects one tab with the other. A match assembly of the present invention may also include a pair of leg wires individually attached to the tabs and adapted to be connected to a source of electrical energy suitable for firing the initiator.

The tabs of the present match assembly are preferably fabricated from a thin sheet of a metal which can be easily soldered as both the bridge wire and the leg wires need to be attached to the tab. Copper or brass are aptly suited to this use. Preferably, at some point above the bottom portion of the tab, the tab members have a portion broader than the bottom portion. Suitably the tab members may be fabricated in a trapezoidal shape. The layer of non-conductive material which separates the tab members may, for example, be paper, fiber, asbestos, or ceramic. The metal tabs and non-conductive layer are suitably in the form of a laminate being adhesively joined. The bridge wire which connects the tabs is preferably a thin wire of high electrical resistance.

The plug of semi-conductive material is preferably comprised of a mixture of a finely divided metal and a nonc-onductive matrix material. Although finely-divided metals, such as copper, lead, and iron may be utilized, finely-divided aluminum has been found to be particularly effective as the metal component. Finely divided metal oxides may be substituted for a portion of said metal component to achieve the desired results. In the term metal oxides as used herein is included mixed metal oxides such as chromates, manganates and stannates. Various metal oxides may be used for this purpose, for example, Pb O Sn O Fe O MnO CuO, K Cr O and BaCrO While insulating materials suc has polyethylene may be used, wax has been found to be particularly satisfactory as the non-conductive matrix material. Suitably the wax has a relatively high melting point, for example, natural Waxes such as beeswax and carnauba, and synthetic waxes such as Acrawax are useful in the present invention. Preferably the finely divided metal and metal oxides are of a size that will pass a number 100 U.S.S. screen. Preferably the semi-conductive material contains between about 80% and about 99% by weight of the finely-divided metal component and between about 1% and about 20% wax. Up to about 50% of the metal component may be substituted with one or more suitable metal oxides without reducing the susceptibility of the subject initiators to static electricity or malfunctions due to arcing. In most practical instances where a metal oxide is to be incorporated from about 0.5% to about 50% of the metal component is replaced with one or more metal oxides. The semiconductive material may be produced by initially thoroughly mixing a finely divided form of the components in their desired proportions, pelleting the mixture and then granulating the pellets preferably through a 20 mesh U.S.S. screen. The granulated mixture is suited to pressure forming operations and may be easily formed into any desired shape.

In order to maintain close electrical contact and to insure close contact in a mass produced item the matchbody comprising the tabs and the non-conductive material separating the tabs is preferably perforated and the semiconductive material forcefully positioned in the perforation. The semi-conductive material may be forcefully positioned in a perforated mat-ch assembly by placing a perforated match assembly in a suitable fixture that has a top plate and a hole therethrough, aligning the plate hole and match perforation, and pressing a loose charge or a preformed pellet of semi-conductive material in the aligned hole and perforation. A pressure in the range of from about 10,000 to about 30,000 p.s.i. has been found to be aptly suited to use in the pressing operation. The size of the perforation in the match assembly may vary due to such variables as the size of the assembly, or the composition of the semi-conductive material. suitably the plug is of a size that will provide a good path for static electricity across the match tabs. Generally, positioned plugs having a cross-sectional area of between about 0.0028 and about 0.0078 square inch and general cylindrical in shape give satisfactory results. Suitably the plug is cylindrical. It may also be preferred, in order to insure close electrical contact, that the plug extend slightly on either side of the match tabs. Generally between about 0.001 and about 0.005" is sufficient. In order to insure a good electrical connection between the tabs, the plug and the leg wires, the leg wires may suitably be soldered directly on the tab and in contact with the end of the plug.

The present invention also contemplates an electric explosion initiator which includes a match assembly in accord with the present invention. Electric initiators generally comprise a metallic shell member, encasing an explosive charge and a match assembly positioned in firing position with the charge. Preferably the explosive charge is comprised of a detonating base charge and a primer charge positioned in initiating relation to the base charge. A match assembly in accord with the foregoing description is positioned in igniting relation to the primer charge. Suitably the initiator has a thin layer of insulating and spacing material, for example, paper, cardboard, or plastic, positioned between the match assembly and the sides of the shell member to prevent physical contact of the match assembly and the shell wall.

The present invention also contemplates a delay explosion initiator which includes a match assembly in accord with the present invention. Generally a delay explosion initiator of the present invention includes a metallic shell, an explosive charge positioned in one end, a primer charge positioned in firing relation to the base charge and a delay element which includes a delay train positioned in firing relation to the primer charge. A match assembly in accord with the present invention is positioned in firing relation to the delay train.

Now referring to the drawings wherein similar numerals denote similar components throughout the several views: FIGURE 1 is a front elevation of an initiator match in accord with the present invention; FIGURE 2 is a side view partly in section of the match shown in FIGURE 1; FIGURE 3 is a sectional elevation of an electrical explosion initiator containing a match of the present invention, and; FIGURE 4 is a sectional elevation of a delay electrical explosion initiator containing a match of the present invention.

Looking now in detail at the drawings, and in particular, at the match shown in FIGURES 1 and 2.

Metallic match tabs

11 and 13, suitably of a trapezoidal shape, have a narrowed bottom portion 15.

Leg wires

17 and 19 are attached to tabsll and 13 suitably by a soldered joint such as 21. A layer of nonconducting material 12 electrically separates the tabs. A bridge wire 23 elecagape-A47 contact therewith is amatch composition 25 forming a match head 27. Suitably the match composition is molded around the bridge wire. The match composition may be applied to the match assembly by suspending the match composition in a lacquer, such as nitrocellulose,

which acts as a binder and leaves a flammable residue on drying, and dipping the bridge wire end of the match assembly in the suspension. Upon removing the match assembly from the suspension a layer of the suspension clings to and covers the bridge wire. On drying a match head is formed. After the first layer, subsequent layers maybe applied. Suitable materials for the match ignition composition include, for example, cuprous acetylide, diazodinitrophenol, lead mononitrorescorcinate, mixtures of lead mononitroresorcinate and potassium chlorate, and

silver or lead azides.

A plug of semi-conductive material 29 extends through tabs 11* and 13 and non-conducting layer 12-. Suitably plug 29 extends slightly beyond the confines of the match tabs in' order to insure good electrical contact with

tabs

11 and 13 and

leg wires

17 and 19. Plug 29 is suitably comprised of a finely-divided metal, for example, aluminum, or a combination of aluminum and a suitable metal oxide suspended in a matrix of a relatively high melting point wax, for example, Acrawax.

FIGURE 3 is a sectional elevation showing a match assembly of the present invention incorporated in an,

electric explosion initiator. Shell 30 suitably of a metal such as copper, brass'or aluminum, contains a base charge 31 in one end thereof. Base charge 31 is suitably a detonable material for example, pentaerythritol tetranitrate or tetryl. A primer charge 33 is positioned adjacent and in detonating relation to the base charge 31. Primer charge 33' is suitably comprised of mannitol hexanitrate or diazodinitrophenol. Adjacent and in detonating relation to the primer charge 33 is a match assembly similar to that shown in FIGURE 1 and FIGURE 2. A paper cylinder 35 is positioned between the inside wall of shell 30 and the match assembly in order that physical contact between the shell wall and the match assembly is prevented.

Leg Wires

17 and 19 are connected with the match assembly and extend out of' shell 30 through a sealing plug 37" suitably'of nubberor plastic.

FIGURE 4 is a sectional elevation showing a match assembly of the present invention incorporated in a delay electric explosion initiator. The components of the initiator shown in FIGURE 4 correspond with the components of the initiator shown in FIGURE 3 except that adjacent and in firing position to primer change 33 is a delay element 43 containing a delay powder train 45, for example, a mixture of a powdered mixture of a zirconium-nickel alloy and red lead. The match assembly ispositioned in-firing relation to the delay powder train45.

In operation any ditference of high potential existing

betweeri'the leg wires

17 and 19 is equalized by a passage of potential through plug 29, rather than through bridge wire 23. The present invention also provides a discharge path for high potential existing on the leg wires-plug circuit through the match tabs points, for example, 339 and 41, through insulation 35 to the inside of metallic shell 30. The high potential path made available elfectively circumvents the bridge wire and facilitates the dissipation of the potential charge in a harmless manner, that is, from the outside shell wall to ground either directly or by contact with a grounded object.

When exposed to elevated temperature conditions which prevail within an initiator when electrical arcing occurs, the semi-conductive plugpartially melts and provides a path of low resistance between the leg wires. The path available to the electrical current aborts violent arcing conditions within the initiator and thereby prevents malfunction of the initiator.

Table I shows the results of .a series of comparative electrostatic tests conducted using initiators containing.

semi-conductive plugs of the prior art and initiators'containing plugs inaccord with the present invention. The prior art detonators contained a plug of semi-conductive materials positioned within the confines of the detonator shell. The plug was positioned so that it surrounded and was in intimate contact with bared portions of the leg wires and extending to close proximity with the inside shell wall. The plug is spaced from the shell wall by a distance substantially less than the distance between-either of the leg wires and the shell wall in the locus of the ignition composition. Thus, a static charge may be conducted to the edge of the semi-conductive plug-body and allowed to discharge to the shell Wall. In this manner the static charge may be grounded to the shell outside the locus of the ignition composition. Testseries 1 shows the results of a series of tests conducted on prior art initiators. Test series 2 shows the results of similar tests on the initiators of the present invention. The tests were made to determine the sensitivity of the initiators to an electrostatic charge. Each initiator of'each series was separately tested by electrically connecting it to a condenser previously charged by a high potential power source. In carrying out the test, the leg wires of the initiator were shunted and then electrically connected to a source of condenser discharge, the shell of the initiator was electrically connected to a ground source, and" incremental increasing amounts of condenser energy was applied to the shunted leg wires until detonation occurred. The minimum condenser energy required tofire the initiator or, if the initiator failed to fire, the maximum charge which could be' delivered-from the test equipment wasreoorded. For example, in test series 1 shown in Table I, 25 prior art initiators each containing a protective plug comprised of 60% by weight of powdered aluminum in a wax matrix were tested one at a time by connecting. the initiator shell to ground, shunting the leg wires and connecting the shunted leg wires by means of a suitable switch to a condenser previously changed from an electrical source. In test series 1, the initial test energy was 0.5 joule at 10 kv. which was discharged through the detonator to be tested. If the detonator did not fire, the energy test level, using 10 kv., was raised in increments of 0.5 joule testing the detonator at each energy level. The maximum energy test level, using 10 kv., was 5.0 joules (0.10 mfd.).

If the detonator had not detonated when this energy test level was reached, the 0.10 mfd. condenser was charged denser when charged from a 13 kv. source. The highest energy level required'to initiate any one initiator in the group was 8.4 joules. The lowest energy level suflicient to fire one in the group was 1.5 joules. The average amount ofelectrical energy required to fire the series was 5.1 joules. Test series '2 shows the results obtained when 50 initiators of the present invention containing protective plugs made up of by weight of .powdered aluminum in a wax matrix were tested in a similar manner to those in test series 1. It will be noted that 12 initiators of test series 2 did not fire when exposed to an electrical energy level of 11.2 joules, which was the capacity of the static 11.2 joules, thus the actual energy level required to fire the series Would be higher than the 7.7 joules shown in Table I. Test series 3 was carried out in a similar manner and the average energy level required to fire the invalue. In each test a lead plate was placed beneath the initiator and examined after firing to determine the chiciency of the initiator. The firings were judged from good to bad by designations of from A to F in the plate itiators was calculated on the same basis as Test Series 2 tests. Test series 16 was conducted in a similar manner TABLE I Energy (Joules) No. of Type of Plug No. Tested no-fires at 11.2 High Low Average joules Test Series 1 Leg Wires 60/40, aluminum-wax s 25 8. 4 1. 5 5. 1 Test Series 2 Match head 90/10, aluminum-wax 50 1. 7. 7+ 12 Test Series 3 Match head 95/5, aluminum-wax .s 50 1. 5 5. 8+ 8 In general initiators which exhibit 0% detonation at the energy level of 1 joule at 10 RV. are considered to be to test series 1315, and 1723, except that a 420 volt power line source of electrical energy was utilized.

TABLE III Type or Plug No. Tested Potential Amperage Results Test Series 13 Leg wires 60/40 aluminum-wax. 50 240 10 4 plug blowouts.

Normal functioning all Test Series 14 Match head 95/5 aluminum-Wax. 25 2A0 10 A plates. Test Series 15 Match head 95/5 aluminum-wax. 50 240 Nirmial functioning all p a s. Test Series 16 Match head 95/5 aluminum-wax. 50 420 15 Norlnial firing all A p a es.

TABLE IV Test Series 17 18 19 20 21 22 23 Percent Aluminum 75 75 75 75 75 75 75 Percent Metal Oxi 20 2O 20 20 20 20 20 Metal Oxide SnOz M1102 CuO PbsOl FeaOl K2Or 01 BaCrOr Percent Acrawax O 5 5 5 5 5 5 5 Number of Initiators Tested- 25 25 25 25 25 25 25 Potential (Volts A.C.) 230 230 230 230 230 230 230 Amperage 10 10 10 10 10 l0 10 Results 1 Normal firing, no blowouts, all A plates. free from the danger of accidental firing due to extrane- Having thus described the invention, what is claimed ous electricity normally encountered during their use. is. Table II shows the results of a series of tests using 1. Amatch assembly comprising initiators containing plugs in accordance with the presa pair of conductive tabs having a bottom portion, ent invention wherein the leg wires of each initiator were said tabs separated by a layer of non-conductive mashunted and electrically connected to a source of con terial, denser discharge and the shell of the initiator was eleca bridge wire connecting said tabs along said bottom trically connected to a ground source. The results in portion, Table II were obtained by exposing the initiators to an an ignition composition in ignitable position with said energy of 1.0 joule at 10 kv. bridge wire,

TABLE II SHUNT-TO-SHELL STATIC TESTS AT 1 JoULE-m KV. 0F ALUMINUM-METAL OXIDE-AORAWAX o COMBINATIONS Test Series 4 5 6 7 8 9 10 11 12 Percent Aluminum 95 75 75 50 75 75 75 70 70 Percent Metal Oxide 20 20 45 20 20 2O 25 25 Metal Oxide Pbafi S1109 FeaOl F0304 0110 M110: K Or O1 BaOrO; Percent Acrawax C 5 5 5 5 5 5 5 5 5 Number of Initiators Tested- 25 25 25 25 25 25 25 25 25 Percent Firing 0 0 0 0 0 0 0 0 0 Number Failing to Fire 25 25 25 25 25 25 25 25 25 Tables III and IV are compilations of test results in said tabs havng a portion broader than said bottom regard to the arc-resistance. Test series 1423 are test portion, results of initiators of the present invention. In test said tabs and said non-conducting material having a series 13, shown in Table III, 50 prior art initiators were perforation therethrough, and evaluated. Table IV is a compilation of test results of a plug of semi-conductive material positioned in said the arc resistance of initiators containing a plug of the perforation in contact with each member of said pair present invention comprising a mixture of aluminumof tabs. metal oxide and wax. In each test series of Tables III 2. The match assembly of claim 1 wherein and IV each initiator was individually tested by applying the semi-conductive material is a mixture of a finely an electrical current from a 60 cycle AC. power line to divided metal and an insulating material. the leg wires for a period of 5 seconds. In each test 3. The match assembly of claim lwherein series, a rheostat was connected in series with the test the semi-conductive material comprises a mixture of initiator to initially adjust the current to the desired aluminum and an insulating material containing between about 80 to about 99% by weight of aluminum.

4. The match assembly of claim 1 wherein the semi-conductive plug extends in an outward direction beyond the surface of said tabs.

5. The match assembly of claim 1 wherein the semi-conductive plug has a cross-sectional area between about 0.0028 and about 0.0078 square inch.

6. The match assembly of claim 1 wherein the semiconductive material is a mixture of a finely divided metal, a finely divided metal oxide and an insulating material.

7. The match assembly of claim 1 wherein the semiconductive material comprises a mixture of aluminum, a metal oxide and an insulating material.

8. The match assembly of claim 7 wherein the metal oxide is selected from the group consisting of Pb O SnO F6304, C110, M110 K2CI'207 and BaCrO 9. The match assembly of claim 1 wherein the semiconductive material comprises a mixture of from about 45% to about 98.5% of aluminum, from about 0.5% to about 50% metal oxide and from about 1% to about 5% wax.

10. An electric explosion initiator comprising a shell member containing an explosive charge positioned in said shell member,

a match head positioned in firing relation to said charge,

said match head comprising a pair of conductive tabs having a bottom portion,

said tabs separated by a layer of non-conductive material,

said tabs and layer of non-conductive material having a perforation therethrough,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material in close physical contact with a plug of semi-conductive material positioned in said perforation in contact with each member of said pair of tabs,

a pair of leg wires entering said shell member,

separate members of said pair of leg wires electrically connected to separate members of said pair of tabs, and

a non-conductive shield positioned between said pair of tabs and said shell wall.

11. The electric explosion initiator of claim wherein the semi-conductive material is a mixture of a finely divided metal and an insulating material.

12. The electric explosion initiator of claim 10 wherein the semi-conductive material comprises a mixture of aluminum and an insulating material containing between about 80 to about 99% by weight of aluminum.

13. An electric explosion initiator comprising a shell member containing an explosive charge positioned in one end of said shell member,

a match head positioned in firing relation to said charge,

said match head comprising a pair of conductive tabs having a bottom portion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

said tabs and said non-conducting material having a perforation therethrough, and

a plug of semi-conductive materials positioned in said perforation in contact with each member of said pair of tabs,

a pair of leg wires entering said shell member,

14. The initiator of claim 13 wherein the plug in said match extends in an outward directio beyond the surface of said tabs.

15. The initiator of claim 13 wherein the semi-conductive material is a mixture of a finely divided metal and an insulating material.

16. An electric explosion initiator comprising a shell member containing an explosive charge positioned in said shell member,

a delay element positioned in firing relation to said charge,

a match head positioned in firing position to said delay element,

said match head comprising a pair of conductive tabs having a bottom portion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

a pair of leg wires entering said shell member,

17. The electric explosion initiator of claim 16 wherein the semi-conductive material is a mixture of a finely .divided metal and an insulating material.

18. The electric explosion initiator of claim 16 wherein the semi-conductive material comprises a mixture of aluminum and an insulating material, said mixture containing between about and about 99% by weight of aluminum.

19. An electric explosion initiator comprising a shell member containing an explosive charge positioned in one end of said shell member,

a delay element positioned in firing relation to said charge,

a match head positioned in firing position to said delay element,

said match comprising a pair of conductive tabs having a bottom portion,

said tabs separated by a layer of non-conductive material,

a bridge wire connecting said tabs along said bottom portion,

an ignition composition in ignitable position with said bridge wire,

said tabs having a portion broader than said bottom portion,

1 l 1 2 a plug of semi-conductive material positioned in said the semi-conductive material is a mixture of a finely perforation in contact with each member of said pair divided metal and an insulating material. of tabs, a pair ofleg wires entering said shell member, References Cited by the Exammer separate members of said pair of leg Wires electrically 5 UNITED STATES PATENTS connected to separate members of said pair of tabs, 1,868,224 7/1932 Schurmann 2,173,270 9/1939 Burrows 102-28 a non-conductive shield positioned between said pa1r 2,974,590 4/1961 Ram;r 1O2 28 of tabs and Said shell wall- 3,041,972 7/1962 Ball 102-2s 20. The initiator of claim 19 where-in 10 3 194 160 7/1965 Spillane et a1 102-28 the plug in said match extends in an outward direction beyond the Surface of Said tabs SAMUEL FEINBERG, Przmary Examiner.

21. The initiator of claim 19 wherein V. R. PENDEGRASS, Assistant Examiner.

Claims

1. A MATCH ASSEMBLY COMPRISING A PAIR OF CONDUCTIVE TABS HAVING A BOTTOM PORTION, SAID TABS SEPARATED BY A LAYER OF NON-CONDUCTIVE MATERIAL, A BRIDGE WIRE CONNECTING SAID TABS ALONG SAID BOTTOM PORTION, AN IGNITION COMPOSITION IN IGNITABLE POSITION WITH SAID BRIDGE WIRE, SAID TABS HAVING A PORTION BROADER THAN SAID BOTTOM PORTION, SAID TABS AND SAID NON-CONDUCTING MATERIAL HAVING A PERFORATION THERETHROUGH, AND A PLUG OF SEMI-CONDUCTIVE MATERIAL POSITIONED IN SAID PERFORATION IN CONTACT WITH EACH MEMBER OF SAID PAIR OF TABS.