US2762302A - Electric detonator - Google Patents

Description

Sept. 11, 1956 A. MacLEOD 2,762,302

ELECTRIC DETONATOR Filed Nov. 16, 1951 INVENTOR. NORMAN A. MACLEOD,

BY QK W ATTORNEY United States Patent Ufice Patented Sept. 11, I956 7 2,762,302 ELECTRIC DETONATOR Norman A. MacLeod, Altadena, Calif Application November 16, 1951, Serial No. 256,805

' *3 Claims. or. 102 zs (Granted under Title 35, U. s. Code 1952 a... 266) 1hisinvention relates to an electric detonator for explosives, and more particularly to a gap assembly for use in detonators of the type wherein an electrical current bridging a gap initiates an explosion in'adjacent explosive material; V p

' 'It is well'known in the art thatdetonators can be made using two conductors separated by a gap. The old method of manufacture employs two insulated wires which are-twisted-together and the twisted portion embedded in a plastic:matrix. A portion of the matrix is ground off, leaving two exposed wire ends on a plane surface and separated by the insulation on the wires. The old method has disadvantages since the individual twisting and matrixing of each pair of wires results in lack of uniformity; the twist is difiicult to control because the wire ends tend to spring out of position; it is difficult to matrix a twisted wire pair without forming cavities; the round wires used provide a poor spark discharge shape; and it is possible to attain a small gap only by using wires with a thin separating insulation which is weak mechanically.

In one form of the present invention, a current conducting foil is positioned between two strips of nonconductive material to form a composite strip. The material used may conveniently be a plastic such as vinyl or acrylic resins. Two of the composite strips are then joined with their foil edges opposed so that the distance between the strips of foil controls the gap distance at the end surface. A convenient method of manufacturing the gap assembly is to form the composite strips in rather long lengths, then cement two of them side by side with their foils in the same plane, or in parallel adjacent planes, and cut the long assembly into short sections which are of uniform cross section throughout.

It is an object of this invention to provide a simple, sturdy electric detonator in which optimum gap shapes and gap dimensions can be precisely reproduced.

Other objects and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following description.

The instant invention is illustrated diagrammatically in the accompanying drawings, in which:

Fig. 1 is a perspective view of a gap assembly embodying the invention;

Fig. 2 is a similar view of a modified form of the invention;

Fig. 3 is an end view of the assembly wherein a plastic strip is positioned between the two conductors to enlarge the end gap by a controlled amount;

Fig. 4 is an end view of a gap assembly in which one electrode is metal foil and the other electrode is a wire;

Fig. 5 is a longitudinal view, partly in section, of a detonator including a further modified form of gap assembly; and

Fig. 6 is a view in perspective of the rear end of a gap assembly showing a manner of connecting the same to a firing current.

Referring first to the embodiment shown as Fig. 1, a conductive foil 10 is placed between strips of plastic 12 to form a composite strip. In all of the figures of the drawing, the thickness of the foil 10 is exaggerated for clarity, ..but it will be understood that the thickness is such as is implied in the term foil. Two of such composite strips are then bonded together by means of insulating cement 13 with their adjacent foil edges opposed as shown in Fig.1. The long assembly is then cut to convenient lengths toform gap assemblies, and the end surface of each gap assembly is then ground or polished'to produce a. uniform surface. The'gap distance is controll'edby the thickness of the cement. bond 13.

The embodiment shown in-Fig-. 2. is similar tothat shown inFig. 1, except that in Fig. 2 the two composite strips are. displaced laterallylfrom each other in order to increase the gap between foil strips 10 where a larger end gap is desired.

In Fig. 3 is shown the use of opposing electrodes10 separated by a non-conducting. film 15, bonded by cement films 13. It Will be seen that the gap distance can be accurately controlled by using film of any given thickness as a spacer. Except .for the presence of a spacer inthe zone, which in the embodiments heretofore described is occupied by cement only, the structure is identical with that shown at Fig. 1.

Fig. 4 shows an assembly containing foil 10 as one conductor and a wire 17, embedded in a plastic strip 27 and having a thickness greater than that of the foil, as the other conductor. In this modification, the foil furnishes the desirable point electrode and the relatively large area of the wire enables the gap size to remain nearly constant even though the two strips may be slightly out of alignment; a failure to properly align two foil-andplastic strips of the type shown in Fig. 1 may result in an undesired gap distance. The wire may be flattened in cross section as shown, in order that displacement of the plastic strip 27 will not greatly affect the length of the gap. 7

The detonator shown in Fig. 5 comprises a gap assembly 23 which is similar to that shown in Fig. 1 except that it has been turned down to cylindrical shape. A cap 16, of known design and of insulating material, is fitted over the gap assembly and contains an initiator explosive 18 such as lead azide. If desired, a film 20 of graphite or the like may be applied to the polished end of the gap assembly. In order to obtain a better bond between the elements, the foil 10 may be formed with perforations 22, into which the plastic material 12 may be pressed while hot, as shown. Similar bonding means may be employed in the other forms of the invention shown in the drawing.

Fig. 6 shows the rear end of a gap assembly of the type shown in Fig. 3, and indicates how the electrical current may be supplied thereto to fire the charge. In the example shown, bores 30 are drilled in the respective composite strips in the plane of the foil strips, to receive metal plugs 32 which conduct current to the respective foil strips. Alternatively, female connectors may be used with any convenient receptacle to provide sturdy reliable connections which can be rapidly made or broken.

The forms of the invention shown in Figs. 1-5 may be provided with any suitable connectors, such as the plugs 32 shown in Fig. 6. The current is prevented from traveling from one conductor to the other by the cement bond 13 except at the gap at the end of the assembly. The current flow across the gap serves to initiate explosion of explosive material positioned adjacent to the thin graphite film which, though not necessary to the operation of the gap assembly, aids in establishing a current flow across the gap.

It is possible to use foil and plastic strips of indefinite length and thus prepare many gap assemblies in a rela- I tively few operations. The structure resulting when two long composite strips are cemented together is divided into a number of duplicate assemblies by a simple cutting Operation. Since the significant dimensions are established w before the cutting operation .takes place, gap assemblies wise with a fixed distance between adjacent edges ofsaid conductors controlled by the thickness ofv the cement,

' and forming a plane end surface bounded by onepair of formed by the process will have reproducible character-' I istics as detonators.

Obviously'many modifications and variations of. the 10 present invention are possible in the light of the above teachings. For example, the foil 10 of Fig. 1 may be the plastic or by any conductor having the requisite shape and uniform cross section. As another example, the

' graphite film bridging the electrode gap may be replaced by any suitable conductive coating'or by a bridge \wire.

' replaced by a metallic film deposited. on the surface of It is, therefore, to be understood that within the scope The invention described herem may be manufactured and used by or for the Government of the United States I of America for governmental purposes without the pay- I ment of any royaltiesthereon or therefor.

.WhatisclaimedisL I j f 1. In a method for the manufacture of detonator gap assemblies, the steps comprising forming a composite longitudinally uniform stripincluding an electrical con- 7 ductor bondedbetween strips of substantially rigid plastic insulating material, cementing two of said units lengthofvth'e appended claims the invention maybe practiced otherwise than as specifically described. 20

conductor ends.

2. The invention defined in claim 1 comprising in addition the step of cutting the cemented composite strips into a plurality of gap assemblies identical in cross section and having plane ends.

3. In an electrical detonator, a gap assembly comprising :two composite longitudinally uniform units each'including two strips of plastic material separated bymetallic foil and terminating in a common plane, and insulating I adhesive securing said units together and maintaining the adjacent edges of the foil at the ends of; said units opposed to each other and in predetermined spaced relation.

7 7 References Cited in the file of 'this'patent UNITED STATES PATENTS 148,338 'Varney -1. Mar. "10,1874 1,542,825 Newton June 23, 1925 I 7 1,926,842 Dubilier Sept. 12, 1933 2,437,153 Cohan Mar. 2,, 1948 2,619,443 Robinson Nov. 25-, 1952 2,654,060 Stovall et a1. Sept. 29, 1 953 FOREIGN'PATENTS 7 527,290 :France "a July 21, 1921 969,709 I 7 France May I-il, 1950

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