US2696191A - Electrically operated primer - Google Patents

Description

INVENTOR WILLIAM E. SHEEHA/V ATTORNEYS FIG. 2

Dec. 7, 1954 w. E. SHEEHAN ELECTRICALLY OPERATED PRIMER Filed Oct. 1'7, 1951 Unite States Patent ELEoTRrcALLY OPERATED PRIMER William E. Sheeh'an, Silver Spring, Md.

Application October 17, 1951, Serial No. 251,806 1 Claim. or. 102- 865 (Granted under Title 35, U. s. code 1952 mazes This invention relates to explosive priming devices, and more particularly to an improved electrically ac tivated igniter for initiating the explosion of larger charges of explosives.

Primers of the above character usually comprise a closed cup adapted to be secured in an explosive device adjacent the main explosive or propellant charge and contain a highly sensitive ignition composition and a flash charge. The ignition composition may be gun cotton or other sensitive compositions known in the art and is usually formed about a single high resistance filament known as a bridge wire, which is connected in the electrical firing circuit. The arrangement is such that as the bridge wire is heated upon closing of the firing circuit the sensitive composition ignites and develops sufficient heat to set off the flash charge which in turn fires the main explosive or propellant charge of the device with which the primer is used.

Prior art primers of the above character make use of a lead-in wire to connect a bridge wire to an external source of electricity and as such are subjetc to scaling problems about the lead-in wire or wires which may result in the entrance of moisture into the ignition compound, thus increasing the probability of misfires or adversely affecting the predetermined time delay, before teh main or propellant charge is fired. Another disadvantage in such devices resides in the possibility of one or both of the lead-in wires being broken thereby preventing the establishment of an electrical circuit at the desired time to fire the ignition charge. It will also be apparent that the single loop bridge wire which is usually made of flimsy material may be broken during rough handling, thus further increasing the percentages of misfires or duds. Since the bridge wire is inaccessible for inspection such a defect will go unnoticed until an attempt is made to fire the explosive charge.

Although the number of misfires encountered in a series of explosioins may be relatively small, each misfire constitutes a potential source of serious injury or possible death to the individual whose task it is to remedy the fault. The removal of the explosive material is extremely dangerous especially in blasting operations because the explosive material may be difficult to locate in some instances and may blow up accidentally due to various causes while searcihing for it. In ordnance equipment a misfire will reduce the fire power of the weapon used or in cases of automatic weapons the weapon itself may be jammed, thus subjecting those whose lives are dependent upon the operation of such weapons to imminent danger.

The present invention avoids the disadvantages of prior art devices of this character by providing a single electrode which forms an electrical circuit through a plurality of bridge wires and then to ground through the surface of the primer and also permits the use of a plurality of bridge wires which are readily aflixed within the igniter cup so as to prevent misfires due to poor electrical contact within the igniter itself.

With the foregoing in mind it is an object of the present invention to provide an igniter which affords unform firing results by the establishment of mamixurn contact between the initiating composition and the electrical bridge wires which serve to ignite the composition.

Another object is the provision of a preassernbled hermetically sealed igniter element for use in detonator primers which is positive in action, rugged in construction, compact in design, and economical to manufacture.

Still another object is to provide an igniter element which lends itself to quantity production.

Yet another object is the provision of an igniter bridge assembly which may readily be varied in size to provide for different ignition requirements.

These and other objects, and their attendant advantages will become more apparent from the following description when read in conjunction wdith the accompanying drawings in which:

Fig. 1 is a longitudinal sectional view of an electrically actuated primer illustrating an embodiment of the present invention;

Fig. 2 is a sectional exploded view of a portion of Fig. 1 showing the detailed arrangement of parts that make up the electrical primer of the present invention; and

Fig. 3 is a perspective view of the igniter bridge assembly.

Referring now to the drawings wherein like numerals designate the same parts throughout the several views and more particularly to Fig. 1 wherein there is disclosed a casing 10 which is externally threaded for attachment to a projectile or any other great charge of explosive and internally threaded to receive a locking sleeve 11 which is adapted to hold a preassernbled electrical ignition element or primer designated generally by the numeral 50, firmly in place in a cavity formed in the casing 10. The electrical ignition element comprises a flanged electrode 12 the neck portion of which extends through an opening in the base 13 of the casing it and is insulated fromthe edges of the opening by an annular insulating sleeve or bushing 14. The electrode 17. is made of brass or any suitable electrically conductive material and is formed with an enlarged head portion 15 which is mounted within a metallic primer cup 16 and insulated therefrom by an apertured insulating disc 17 and a sleeve 18 composed of fiber, plastic, or any other insulating material and the neck portion of the flanged electrode 12 extends through the cup 16 and through an opening in the base of the casing 10. The primer cup 16 serves to hold the elements of the primer in position and also to provide a ground connection through the casing 10.

In juxtaposition and in electrical contact with said enlarged head portion 15 and insulated from the cup 16 is a bridge assembly shown in Fig. 3 which comprises a pair of annular laminae or washers 19 and 20 made of electrically conductive material such as copper, axially separated by and bonded to an insulating ring 21 made of laminated phenolics, or other suitable insulating .material. Connecting the washers or laminae 19 and 20 are one or a plurality of looped bridge wires 22 made of a high resistant material such as platinum iridium alloy, nichrome tungsten or other similar materials which wires are attached to the inner periphery of said washers by soldering, brazing, staking or other suitable means. The looped portions of bridge wires 22 extend longitudinally through a chamber or cavity 23 formed by the assembled washers 1Q and 2th and ring 21. The chamber or cavity 23 is filled with a nonconductive igniter composition 24 such as gun cotton or diazodinitro phenol surrounding and in intimate contact with the looped portions of wires 22 which serve as igniters for the composition. An an alternative the chamber 23 may be filled with a conductive igniter composition such as lead styphnate-graphite which will eliminate the use of the bridge wires 22. The chamber 23 is sealed on the left by the flange 15 of the electrode 12 and on the right by a relatively thin metallic disc 25 of electrically conductive material. Seated against the disc 25 is an ignition spacer sleeve 26 formed of brass or other conductive material and having an annular opening therein which carries a flash charge 27 of black powder or other suitable material to be set off by the igniter composition 24. The flash charge chamber is closed at the right end by a second metallic disc 28. The disc 28 is in electrical contact with an inturned flange portion 29 of primer cup or housing 16 which is formed by crimping or other similar means so as to complete an electrical circuit from a source (not shown) through electrode 12, washer 19,

a bridge wire or wires 22, washer 20, disc 25, sleeve 26, disc 28, primer cup 16, and thence to the grounded casing 10.

The primer element 50 is assembled separately from casing and hermetically sealed by coating an annular space 30 with Bakelite or any other suitable sealing compound and adding a fillet of the same material at the junction of flange 29 and disc 28.

The assembled primer element 50 is inserted in casing 10 and held in position by locking sleeve 11 as disclosed above. Booster charge 31 is added in a chamber of the locking sleeve 11 and the chamber closed off by an exteriorly threaded cylinder 32 having apertures 33 in the walls thereof which permit the flash of booster charge 31 to reach a propellant charge (not shown). The assembled casing 10 and primer element 50 are thenplaced in contact with a large charge of explosives or inserted in an ordnance sleeve and ignited by closing any well known firing circuit. The closing of the circuit causes current to flow through the elements as described above which, due to the high resistance of bridge wires 22, produces sufiicient heat in the wires to ignite the com position 24. The ignition of composition 24 will burn through disc 25 to explode flash compound 27 which in turn burns through disc 28 to explode the booster charge 31 thereby setting oi the large charge of explosives.

While the device disclosed herein is a preferred embodiment of the invention it is to be understood that the invention may be embodied in other forms without departing from the spirit or scope of the invention as defined by the appended claim.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

An electrically operated primer for firing a propellant charge comprising; a metallic cup, an electrode having an enlarged head portion mounted partially within said cup and insulated therefrom and a neck portion extending beyond said cup for connection to a source of electricity, an electrically conductive annular lamina in juxtaposition and in electrical contact with said electrode and insulated from said cup, a second conductive annular lamina spaced axially from the first lamina and insulated from said cup, an insulating ring disposed between said conductive laminae, said laminae and said ring forming a cavity, a first igniting composition charge in said cavity, a plurality of high resistance loop bridge wires spaced from each other on the inner periphery of said laminae for igniting said first charge electrically, the ends of said wires being connected to said laminae and a portion of said wires extending longitudinally through said cavity in contact with said first charge, a first conductive disc in electrical contact with the second lamina and enclosing one end of the cavity, an electrically conductive ignition spacer sleeve seated against the first disc and having an annular opening therein, a second flash composition charge within said annular opening, said first disc and the sleeve being insulated from the cup, a second destructible conductive disc in electrical contact with the spacer sleeve and the cup for enclosing the annular opening containing the second charge, and means on said cup in electrical engagement with the second disc, said means restraining axial movement of the component parts to maintain operative engagement.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 520,116 Mason May 22, 1894 676,219 Bryant et a1 June 11, 1901 1,084,745 Lindsay Jan. 20, 1914 1,313,801 Doran Aug. 19, 1919 2,142,583 Yarbrough Jan. 3, 1939 FOREIGN PATENTS Number Country Date 4,449 Great Britain of 1910

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