US2431871A - Electric explosion initiator - Google Patents

Description

Dec. 2, 1947.

D. D. HUYETT ELECTRIC EXPLOSION INITIATOR Filed Oct. 26, 1940 Patented needs, l7

' umreo' srAre Emerald EXPLOSION lm'm 'roa Daniel D. Huyett, Wilmington, Del., easier to Atlas Powder Company, Wn, libel. a

corporation of Delaware Application October 26, 1940, Serial No. 362,971

' Claims. (Cl. 102-28) This invention relates generally to electric explosion initiators and more particularly to a novel construction of such initiators.

Exnlosion initiators heretofore used for initiating blasting agents such as black powder, dynamite and the like, have been formed by assembllng independent units including leg wire, plug and shell units. The leg wire units have been covered with various kinds of insulating materials, principally cotton coverings impregnated with various hydrocarbon compositions and more recently with a plastic which is extruded onto the bare leg wires. Compositions used for producing the plugs have consistedof various materials such as sulfur cements, lead. mineral resins like. pitch or asphalt, rubber. polyvinyl products or mixtures and the like. The shells have uniformly been constructed of metal. In accordance with the conventional practice such explosion initiators are assembled by placing the explosive composition in the shell, forming the plug about the leg wires adjacent the ignition element, inserting the leg wire and plug assemb y into the open end of the charged shell and sealing this assembly therein by a tight fit or if necessary by using moltensulfur, pitch, asphalt, or the like as a sealing medium.

In such assemblies the plug has long been a source of trouble. If the assembly is to be waterproof. the plug must sealingly engage the leg wires and in return be sealingly engaged by the shell of the explosion initiator. The possib lity of leakage exists at both places, that is, adjacent the shell and adjacent the leg wires. Variations in temperature accompanied by consequent expansion and contraction of the plug and/or shell may result in the plug breaking away from the shell. Where the plug is pressure fitted into the shell it may tend to cold flow to such an extent that the plug no longer provides a perfect seal. Furthermore. when rubber or compositions of rubber are used for producing the plug. such materials tend to lose their resiliency resulting in an imperfect seal.

An object of the present invention is to provide a novel explosion initiator assembly which overcomes the foregoing objections.

, Another object of the invention is to provide a novel electric explosion initiator which obviates the use of the conventional end plug closure.

Other objects of the invention will hereinafter more fully appear.

Non-limiting structures constituting preferred embodiments of my invention are illustrated in the accompanying drawings which form a part of this specification and in which:

Figure 1 is a perspective view of an embodiment of the electric explosion initiator, the shell of which has been swaged at a point adjacent one end to form an integral leg wire embracing closure section. a

Figure 2 is a perspective view of another embodiment showing the upper section of the electric explosion initiator, the shell of which has been subjected to a dualswaging process at a predetermined area adjacent one end to form an integral closure section which embraces the leg wires.

Figure 3 is a perspective view of still another embodiment showing the upper section of the electric explosion initiator, the shell of which has been swaged at one end to form an integral leg wire embracing closure section.

Figure 4 is a cross section view of the integral, closure section taken on lines A-A and 0-0 of Figures 1 and 3 respectively.

Figure 5 is a cross sectional view of the integral closure sectlontaken on line 3-3 of Figure 2.

In the electric explosion initiators of the pres-. ent invention there is provided an integral thermoplastic shell closed at the explosive charge end and having its walls extending inwardly at the leg wire end, the inwardly extendingwalls forming an end closure embracing the leg wires positioned therein. Preferably the closure about the leg wires is formed by swaging or hot pressing the wallsof the thermoplastic shell about the leg wires. The legwire end closure of the electric explosion initiators of the present invention eliminates the conventional plug from the assembly. In order to make the explosion initiators of the present invention waterproof it is merely required that the walls of the s'hellabout the leg wires be sealed to the leg wires, as distinguished from sealing a plug to the leg wires and again sealing the plug to the shell. Thus, other things being equal, the opportunity for entrance of atmospheric moisture into the shell is substantially decreased.

The leg wire end closure of the explosion initiators of the present invention may be employed with any type of leg wires such'as bifilar wires, or a two conductor cord or cable. The wire insulation may comprise enamel, thermoplastic ma. terial, cotton impregnated with various hydrocarbon mixtures such as parafin or with natural resins such as pitches or the like.

An embodiment of the leg wire-shell assembly of the present invention is illustrated in Figure 1 wherein i represents a tubular thermoplastic shell wherein is disposed a-charge of explosive composition 2. The two leg wires 3 and i are provided with insulation designated as 5 and 6. At their lower ends, the leg wires are bared at i and 8 to provide for the attachment of an ignition element, indicated in Figure 1 as an electric match 9.

Prior to assemblying such a leg wire and, shell assembly, the explosive composition 2 is charged into the shell. viously been provided with an ignition element such as an electric match or a bridge wire, are

then positioned in the open end of the shell so that a portion of the insulated wires lies within the section of the shell indicated by H and H in Figure 1 that is to be closed by swaging. The thermoplastic shell is then initially sealed at the section of the shell indicated by H and H by a swaging or hot pressing operation which may be accomplished by the concerted movement of a pair of oppositely positioned heated dies, designed to give the same impression. If desired, the section of the shell to be closed by swaging can be preheated before application of the dies. Since thermoplastic materials soften when heated, the shell being constructed of a thermoplastic material softens when it comes in contact with the hot dies used for swaging. By applying pressure with heat the walls of the thermoplastic shell whichcome in contact with the hot dies are forced inwardly and compressed about the leg wires into contact with each other as shown in Figure 4. Thus, a thermoplastic, unitary electric explosion initiator is produced. The plasticity of the shell walls under heat and pressure enables them to form a tight, clasping fit about the leg wires. Thus where only a portion of the leg wires lying within shell portion HE is insulated. the shell walls after swaging are found to conform to the contour of the wires in that the shell walls pinch the uninsulated as well as theinsulated portion of the leg wires.

The application of pressure is desirable as it aids in the setting of the portion of the walls being compressed.

In actual practice it has been found that in many instances waterproof end closures may be formed by the swaging operation hereinabove described. Whether or 'not the end closures will be waterproof in the absence of a subsequent auxiliary sealing operation depends to some extent upon the degree of heat and pressure employed and the nature of the thermoplastic material of the shell and the insulating material of the leg wires. To insure a water-tight closure, a drop of solvent for the thermoplastic material may be introduced into the cup-shaped top ID of the shell and th s liquid-softens and tends to dissolve the inner contacting surfaces of the thermoplastic shell, thereby forming an adhesive layer. Upon evaporation or dispersion of the solvent the adhesive layer dries to seal the shell effectively. To further insure and strengthen the seal, the cup it! may be filled with any suitable thermoplastic material such as asphalt, pitch, resins or the like.

Where thermoplastic insulated leg wires are employed, the thermoplastic insulation lyin within the section designated by H and H and the thermoplastic of the shell forming the said section may be substantially merged together by the heat and pressure employed in the swaging operation or by the use of a solvent for the thermoplastic materials as disclosed above.

While I have shown the leg wires to be two separate wires, it is to be understood that they may be in the form of bifilar wires, or a two-conduc- The leg wires which have presulated with a thermoplastic material, enamel or an impregnated cotton covering as hereinbefore described. The initial closing however is accomplished by a dual. swaging operation; that is, two pairs of hot dies designed to give the same impression, strike the section of the shell indicated by H and H, and form an oblong cupshaped closure II. By applying pressure with heat, the walls of the thermoplastic shell which come in contact with the hot dies are compressed as shown by Figure 5 and form an end closure which embraces the lead wires. It has been found that the walls of many of these shells which have been pressed in juxtaposed relation by the hot dies are firmly sealed. However, to insure a water-tight closure for all shells patterned after the modifications disclosed in Figure 2, an auxiliary sealing step may be invoked whereby a drop of solvent for the thermoplastic is introduced into the oblong cup-shaped top ll of the compressed shell. As heretofore disclosed, this solvent softens and tends to dissolve the inner contacting surfaces of the thermoplastic material and upon complete volatilization serves as a permanent sealing medium in that it merges the compressed walls of the shell to form a homogeneous thermoplastic unitary shell.

Another preferred embodiment of my electric explosion initiator produced by a modified method is illustrated in Figure 3. The shell of this initiator is preferably constructed of a thermotor cord or cable insulated with thermoplastic ma- 'terial, enamel or an impregnated cotton coverplastic material which is molded to leave one end of the shell open. After the shell is charged with an explosive composition and the leg wires, previously provided with an ignition element, have been positioned in the open end of the shell with-- in the section indicated by I and I, an end sealing is effected by the swaging or hot pressing operation previously described. It will be readily understood that the degree of heat and pressure required in the swaging or hot pressing operation depends entirely on the physical properties of the thermoplastic material of the shell and the insulating material of the leg wires. If desired the degree of heat and pressure employed during the swaging operation may be so controlled that the inner contacting surfaces of the thermoplastic shell become sealingly adhesive and form an end closure that is waterproof.

In the assembly of the present invention, any commercially available thermoplastic resins may be used which are compatible and which are water-resistant and electrically non-conductive. I have found such materials as ethyl cellulose, cellulose acetate, "Lucite" (methyl methacrylate) and polyesters of vinyl alcohol well suited for constructing the shell of the device. Materials suitably plasticized, such as ethyl cellulose, modified vinyl halide polymers and polyesters of vinyl alcohol are well suited for coating the lead wires. However, since I have found that leg wires covered with conventional types of insulation including enamel coated wires and cotton covered wires impregnated with mixtures of allphatic hydrocarbons such as parafiln, or mineral resins such as pitch or asphalt may also be successfully employed with my swaged shell plastic type electric initiator, I do not wish to be restricted to the use of plastic coated wires.

Of these thermoplastic materials I have found that the commercially'available resins such as resins formed by the co-polymerization of vinyl chloride and vinyl acetate are highly preferred. In addition to high tensile strength, good dielectric properties and excellent resistance to chemical action and water absorption, these vinyl resins have slight tendency toward cold-flow. This latter property is of'particular advantage in the construction of detonator assemblies of the present invention for the reason that the 1 8 wire end closures ofv the shell are frequently under pressure and unless the material forming the shell has substantial resistance toward coldflow it may tend to deform and therebypermit the entry of atmospheric moisture. Solvents which may be employed in the fin sealing of the electric initiators may be any suitable solvent for the thermoplastic materials to be softened therewith. In general, solvents such as aliphatic esters, aromatic hydrocarbons and ketones may be employed. I have found, however, that benzene or acetone are particularly suitable. v

While I have disclosed structures in which'a .shell of tubular structure is utilized, obviously a shell of another configuration may be employed. In Figure l, I have indicated the explosive charge 2 as a single charge, it is to be understood that this may comprise a plurality of charges with or without capsules, delay fuses and the like. The ignition element 9 has been indicated diaabout the leg wire, swaging said section of .the wall of the shell onto the leg wire to form anend grammatically as an electric match but it is to be understood that any suitable electric ignition element may be substituted therefor.

It is also. within the province of the present invention to moisten the inner walls of the ther- 1. The method of making ,leg wire and shell assemblies for electric explosion initiators which comprises charging an explosive composition into an organic thermoplastic shell, inserting through the open end of said shell an insulated leg wire previously provided with an ignition element, swaging a section of the wall of the shell which lies about the leg wire onto the leg wire to form a cup-shaped end closure embracing said leg wire and introducing a mutual solvent into said end closure for both the insulating material of the leg wire and the thermoplastic material of the shell, the solvent softeningand tending to dissolve the inner contacting surfaces of said shell to form an adhesive layer, which on evaporation of the solvent dries to seal said shell.-

2. The method of making leg wire and shell 6 assemblies which comprises charging an explosive composition into an organic thermoplastic shell, inserting through the-open end of said,

shell, an insulated leg wire previously provided with an ignition element, applying a mutual solvent for both the insulating material or the le wire and the thermoplastic material of the shell to a section of the wall of said shell which lies closure embracing said leg wire.

4. An electric explosion initiator comprising a substantially tubular, organic, thermoplastic shell having a preformed closed end integral with the walls of the shell, an explosive composition charged in said shell against said preformed end, an electric ignition element disposed within said shell in operativeassociation with said explosive composition, a leg wire for said ignition element extending from said ignition element outwardly through the end of said shell opposite said preformed end, a section of the walls of said shell a distance from the end opposite said preformed end being constricted about and embracing said leg wire in a sealing closure, and daring out from.

said constriction in a manner such that a cupshaped portion is formed, said cup-shaped portion being adapted for the reception of a solvent for said organic thermoplastic so as to further seal said end.

5. An electric explosion initiator comprising a substantially tubular, organic, thermoplastic a distance from the end opposite said preformed assemblies for electric explosion initiators which comprises charging an explosive composition into an organic thermoplastic shell, inserting through the open end of said shell, an insulated leg wire previously provided with an ignition element, swaging a section of the wall of the shell which lies about the leg wire onto the leg wire to form a cup-shaped end closure embracing said leg wire, introducing a mutual solvent into said end closure for both the insulating material of the leg wire and the thermoplastic material of the shell, the solvent softening and tending to dissolve the inner contacting surfaces of said shell to form an adhesive layer, which on evaporation of the solvent dries to seal said shell and filling said end closure with a resin to strengthen the seal.

3. The method of making leg wire and shell shaped portion is formed, said cup-shaped por-- tion being filled with a thermoplastic resin which serves as anauxiliary sealing means.

DANEL D, HUYETT.

REFERENCES orrnn The following references are of record in the file. of this patent:

UNITED STATES PATENTS Number Name Date 459,321 Ward Sept. 8, 1891 1,609,598 Austin Dec. 7, 1926 2,237,932 Handforth Apr. 8, 1941 1,094,692 Allison Apr. 28, 1914 2,215,066 Clark Sept. 17, 1940 2,228,878 Johnson Jan. 14, 1941 1,626,118 Olin Apr. 26, 1927 921,049, Wranischar May 11, 1909 2,240,438 Durant Apr. 29, 1941 1,614,210 Schmitt Jan. 11, 1927 139,686 l fiowbray"; June 10, 1873 1,184,746 Hanson May 30, 1916 1,555,823 Bernard Oct. 6, 1925' 954,297 Jackson Apr. 5, 1910 FOREIGN PATENTS Number Country Date 382,247 Great Britain Oct. 20, 1932

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