US2399034A

US2399034A - Electric explosion initiator

Info

Publication number: US2399034A
Application number: US329962A
Authority: US
Inventors: Daniel D Huyett; Fletcher William Earl
Original assignee: Atlas Powder Co
Current assignee: Atlas Powder Co
Priority date: 1940-04-16
Filing date: 1940-04-16
Publication date: 1946-04-23
Anticipated expiration: 1963-04-23

Description

April 23, 1946. D. D. HUYETT EAL Y I ELECTRIC EXPLOSION INITIATOR Filed April 16, 1940 WILLIAM EARL FLETCHER T T E V v 5 0 0m 5 w &m M m m ,D N A ATTORNEY Patented Apr. 23, 1946 ELECTRIC EXPLOSION INITIATOR Delaware Application April 16, 1940, Serial No. 329,962

1 Claim.

This invention relates generally to electric explosion initiators and more particularly to initiators of this type that are used in mining and under-water blasting.

Explosive initiators adapted to be used for initiating the explosion of blasting agents such as black powder, dynamite, and the like, have been formed from a metal shell or case, one end of the shell being closed by a plug through which,

lead wires pass. The end closure or plug has been made from various materials including sulphur cements, lead, mineral'resins such as pitch or asphalt, rubber, and polyvinyl products or mixtures such as mixed polymerisates of vinyl chloride and other unsaturated organic compounds such as acrylic acid esters, maleic acid esters and vinyl acetate.

The lead wires passing. through the plug have been insulated by impregnating cotton coverings. More, recently, the lead wires passing through a rubber plug have been coated with a plastic which is extruded on the lead wires.

Although many proposals have been made for closing these explosive initiator assemblies, access of atmospheric moisture or water to the interior of the explosion initiator thus rendering it ineffective, has not been entirely precluded.

In accordance with the present invention, there is proposed a novel lead wireand plug assembly for electric explosion initiators, said assembly having greatly improved moisture resistance and being otherwise highly advantageous.

An object of the invention is to provide a new lead wire and plug assembly for electric explosion initiators.

Another object of the invention is to provide such an assembly which is unitary and which may be readily produced.

Another object of the invention is to provide such an assembly for the closure of shells of electric explosion initiators, which shells may be constructed of either a thermoplastic material or of the conventional gilding metal.

Still another object of the invention is to pro vide an electric explosion initiator wherein the insulation for the lead wires, the plug assembly and the shell are all of thermoplastic material, the thermoplastic insulation and the plug being merged together at their juncture, and the plug and the shell being merged together at their juncture to form a unitary thermoplastic housing.

Other objects of the invention will hereinafter more fully appear.

Non-limiting structures constituting preferred embodiments of my invention as illustrated in the accompanying drawing form a part of this speciflcation in which:

Fig. 1 is a vertical, sectional elevation of an embodiment of the lead wire and plug assembly;

Fig. 2 is a vertical, sectional elevation of a conventional gliding metal shell type electric explosion initiator having the lead wire and plug assembly of Fig. 1 assembled therein; and

Fig. 3-is a similar section of a plastic shell type electric explosion initiator having the lead wire and plug assembly of Fig. l therein.

Wehave discovered that the objects of our invention may be attained and that a novel lead wire and plug assembly which precludes the entry of atmospheric moisture and water to the interior;

of an electric explosion initiator may be produced by employing a plug of thermoplastic material and lead wires coated with a thermoplastic insulating material, the thermoplastic insulation of the lead wires and the thermoplastic plug being merged together at their juncture, By merged we mean that the contiguous, juncture surfaces unite to form a homogeneous mass. This type of merging of surfaces to form a homogeneous mass is to be sharply distinguished from a merging of surfaces whereby a distinct cleavage surface between the joined surfaces is produced.

This lead wire and plug assembly may thereafter be assembled into the open end of a detonator shell which may be either the conventional glidingmetal type, or, preferably, a shell formed of thermoplastic material. Where the shell is formed of thermoplastic material the plug and shell may be merged together. In this latter embodlment a lead wire plug and shell assembly is produced wherein the thermoplastic insulation of the lead wires and the plug are merged togather at their juncture and the plug and the shell are merged together at their juncture to -form a unitary thermoplastic housing,

An embodiment of the lead wire and plug ass'embly oi the present invention is illustrated in Fig. 1 wherein i represents a tapered plug formed of thermoplastic material. This plug is provided with two small bores 2 and 3, which are drilled or cast into the plug and which may be slightly flared by means of a taper reamer at their lower ends as indicated by 2 and 3'. The two lead wires 8 and 5 are insulated by a coating of plastic designated as 8 and I. The diameter of the lead wireis slightly smaller than the diameter of the bore and the plastic which insulates the lead wire is of such a thickness as to give a tight fit for the insulated lead wire in the bore. At their lower ends the lead wires are bared at 4' portion of the plug.

These lead wire portions lying below the plug are then dipped into a liquid which is a solvent for both the thermoplastic insulating material of the lead wire and the thermoplastic material of the plug. The solvent softens and tends to dissolve the surface of the insulating material contacted by it. These portions of the lead wires are immediately removed from the solvent and drawn upwardly into the plug so that the portion of the insulation so softened lies within the plug as indicated at H and H in Fig. 1 of the drawing. The residual solvent retained on this portion of the lead wires will soften the hole-defining portions of the plug to such an extent as to render such portions semi-fluid and sealingly adhesive with respect to the material coating the lead wires. The solvent is then dispersed either by evaporation or by absorption into the main body of thermoplastic material and the thermoplastic material of the plug lying adjacent bores 2 and 3 and the thermoplastic insulating material of the lead wires lying within the said bores merge together and form a homogeneous mass. Any excess thermoplastic material on the lead wires forms small fillets in the slightly flared ends 2" and 3" of the bores as shown in Figs. 2 and 3 and upon evaporation of the solvent therefrom these fillets structurally strengthen and secure the insulated lead wires adjacent the bores of l the plug.

While we have shown the lead wires tobe two separate wires, it is to be understood that they may be in the form of a two-conductor cord or cable insulated with thermoplastic material, in

which case they may be drawn through a single bore in the plug.

The lead wire and plug assemblies of the present invention are unitary structures which may be assembled with various types of electric exploslon initiators. The plugand insulating material form an effective seal from the shell of the explosion initiator tothe termination of the insulation at the outer end of the lead wires. It can be readily seen that the lead wire and plug assembly is of particular advantage for assembly with explosion initiators which are to be fired under water since the lead wires with their unbroken insulation may be of any desired length and may extend upwardly so that the insulation terminates at a point above the level of the water to prevent any possibility of leakage.

In Fig. 2 the lead wire and plug assembly-0f Fig. 1 is shown assembled with an explosion initiator shell 9 having, an explosive composition therein generally indicated by III. in this modification may be formed of conventional gilding metal.

Prior to assembly of the lead wire and plug with the shell 9, the explosive composition is charged into the shell. The lateral surface of the plug I is moistened with a suitable solvent for the thermoplastic material of the plug and the solvent softens and tends to dissolve the lateral surface of the plug. The lead wire and plug assembly is then forced into the upper end of the charged.

The shell 9 I55 shell 9 to close the same and the lateral surface of the plug contacts the inner walls of the upper end of shell 9, forming the juncture generally indicated by I I.

Where the shell 9 is formed of gliding metal, the softened surface of plug I forms an adhesive which sets upon evaporation of the solvent to form a water.tight joint.

' In the preferred embodiment of the invention as disclosed by Fig. -3, the shell 9 is made of a thermoplastic material which is compatible with the thermoplastic material of the plug I. In assembling this embodiment the solvent employed to moisten the lateral surface of the plug is a solvent for the thermoplastic material of shell 9 as well as a solvent for the thermoplastic of plug I. When the plug I. with its solvent-softened outer surface is forced into the upper end of shell 9', the solvent tends to soften the surface of shell 9' adjacent the juncture indicated at II and upon subsequent evaporation of the solvent the thermoplastic material of shell 9 adjacent said juncture and the thermoplastic material of plug I adjacent said juncture are merged together.

This, in effect, forms a unitary thermoplastic housing comprising the shell, the plug, and the thermoplastic insulating material.

Solvents which may be employed in assembling the thermoplastic insulated lead wires with the plug or in assembling the thermoplastic insulated lead wires and plug assembly with a shell 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. We have found, however, that benzene or acetone are particularly suitable.

In the assembly of the present invention, any commercially available thermoplastic resins may be used which are compatible and which are water-tight and chemically and electrically inert. We have foundsuch materials as ethyl cellulose, cellulose acetate, "Lucite (methyl methacrylate). and polyesters of vinyl alcohol well suited for the plug and shell elements of the device. Materials suitably plasticized, such as ethyl cellulose, modi-.

fled vinyl halide polymers, and polyesters of vinyl alcohol are well suited for coating the lead wires.

Of these materials, we have found that the commercially available resins such as resins formed by the co-polymerization of vinyl chloride andvinyl acetate are hi hly 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 inthe construction of detonator assemblies of the present invention for the reason that the plugs, after insertion into the shell, are frequently under pressure due to the confinement of the surrounding shell and unless the material of the plug has substantial resistance toward cold-flow it may tend to loosen in the shell.

While in Figs. 1, 2 and 3 I have disclosed, as a preferred embodiment of my invention, a structure in which the plug element is externally tapered, obviously. a plug of cylindrical or other form may be employed. In such a construction,

care must be taken to insure snugness of fit of plug and shell surfaces such that moisture may not gain access to the contained detonator composition. Shells of the type with which the present invention is concerned, commonly have a slight flare at their open ends. Where cylindrical plugs are employed, this slight flare scrvw to iacilitate insertion of a plug of such size as to provide a forced fit with the shell proper.

In Figs. 2 and 3 we have indicated the explosive charge id 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 5 has been indicated diagrammatically as a bridge wire but it is to be understood that an electric match or other ignition element may be substituted there-' for.

Other modifications will readily occur to those skilled in the art.

c Having fully described our invention what we claim is as follows:

The method of making lead wire and plug assemblies which comprises boring a plug oi thermoplastic material to provide said plug with a bore oi slightly larger diameter than the diameter of a thermoplastic lead wire with which it is to be employed. threading said lead wire through said bore until a portion or said lead wire lies below and lust adjacent the lower portion of said bore, applying a solvent for both the thermoplastic insulating material oi the lead wire. and the thermoplastic material of the plug to said portion of said lead wire which lies below and just adjacent the lower portion of said bore, dra the wetted insulated lead wire upwardly into said plus, the residual solvent retained on said thermoplastic material of said lead wire softening the hole-defining portions of the plug to such an extent as to render such portions semifiuid and sealingly adhesive with respect to the material coating the lead wires, and merging the contiguous surfaces of said bore and lead wire insulation by dispersing the solvent.