US2965033A

US2965033A - Blasting cap assembly

Info

Publication number: US2965033A
Application number: US616964A
Authority: US
Inventors: Charles F Horne; Edward K Lefren; Edward L Ramer; Roth Julius
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1956-10-19
Filing date: 1956-10-19
Publication date: 1960-12-20
Anticipated expiration: 1977-12-20

Description

Dec. 20, 1960 c. F. HORNE ETAL BLASTING CAP ASSEMBLY Filed 001;. 19, 1956 FIG.2

'III/II FIG. l2b

FIG. 6

FIG. I34

CHARLES F. HCRNE EDWARD K. LEFREN EDWARDL. RAME JULIUS ROTH INVENTORS BY W W- AGENT United States Patent BLASTIN G CAP ASSEMBLY Charles F. Home and Edward K. Lefren, Kingston, N.Y., and Edward L. Ramer, Hockessin, and Julius Roth, Wilmington, Del., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Filed Oct. 19, 1956, Ser. No. 616,964

15 Claims. (Cl. 10228) This invention relates to electric blasting cap assemblies and to their manufacture. In one aspect this invention relates to the electric blasting cap units which when fully assembled are free from conventional wire bundles and can be safely stored, tested or shipped or otherwise handled independently from the wire bundle, and to their manufacture. In another aspect this invention relates to a multi-step method by which electric blasting caps are manufactured, including the steps of disposing bridged pins in an ignition plug in a blasting cap shell, extending pins from the plug and terminating them in close proximity to the end of the shell, and subsequent to requisite handling of the unit thus formed, affixing leg wires to the pins and sealing the juncture with a dielectric material having suitable properties therefor. In still another aspect this invention relates to the use of selected dielectric insulating materials for effecting leg wire-pin seals in the manufacture of electric blasting caps.

Electric blasting caps, or initiators, are employed for detonating high explosives. They contain a detonating charge which is fired by passage of electric current through a pair of lead wires, or leg wires, the latter passed through a plug element in the cap shell and connected therein by a resistance or bridge wire which becomes electrically heated in contact with a heat-sensitive material to cause ignition or detonation of the said material as the case may be.

Various methods have been employed in the manufacture of electric blasting caps. One such method involves casting a sulfur plug around a set of leg wires, the plug being of size for a snug fit in the cap shell; inserting the resulting plug assembly in the shell; pouring a molten asphalt material on the inserted plug of sulfur and around the lead wires extending therethrough, and solidifying same; and then pouring molten sulfur on the asphalt plug and around the lead wires above it, as a topping seal. The leads, as a wire bundle, extend from the cap shell. Another method comprises placing the bridged pins in an ignition plug and then welding or soldering the lead wires to the pins, at a site away from the live cap, and then inserting the resulting plug-wire assembly into the cap shell to render it ready for use.

Electric blasting caps of the low tension type, i.e., with bridge wire assembly and fired by low voltage current, have heretofore been associated with wire bundles attached thereto. This has given rise to difiiculties in respect of storing and handling, particularly in respect of hazards involved as a result of development of static charges on the wire bundles with concomitant accidental firing.

This invention is concerned with electric blasting cap units free from the foregoing ditficulties, and with their manufacture, and with the adaptation of such units for use at any time, as desired.

An object of this invention is to provide electric blasting initiators. Another object is to provide for the manufacture of electric blasting initiators. Another object is to provide electric blasting initiators that can be handled ice as complete units without the usual hazard inherent from development of static charges in the wire bundle, or from stray currents. Another object :is to provide for the manufacture of such units. Another object is to provide dielectric sealing materials for effecting a strong jointure of leg wires with pins of a live electric blasting cap under nonhazardous conditions. Other aspects and objects will be apparent from the accompanying disclosure and the appended claims.

In accordance with this invention a blasting cap is provided which comprises a blasting cap shell; a heatsensitive material in said shell; an ignition plug in said shell in waterproof sealed relation with the interior walls of said shell; electrical conductor pins disposed in said plug and extending into said shell; a bridge wire conmeeting said pins in said shell and in operative communication with said heat-sensitive material to transfer heat to same, when electrically heated, and said pins extending upwardly in said plug and terminating in direct communication with the outside of said shell. Also in accordance with the invention a blasting cap assembly is provided which comprises a blasting cap shell; a heatsensitive material in said shell; an ignition plug in said shell in waterproof sealed relation with the interior walls of said shell; electrical conductor pins disposed in said plug and extending into said shell; a bridge wire conuect ing said pins in said shell and in operative communication with said heat-sensitive material to transfer heat to same, when electrically heated, said pin-s extending upwardly in said plug and terminating in direct communication with the outside of said shell; a leg wire secured to each pin and a dielectric material sealed around each connected lead wire-pin pair and between each said pair in contact with said cap, said dielectric material being capable of effecting a seal with each said leg wire-pin pair to insulate each said pair of wires from the other and from moisture, and being of sufficient strength to withstand failure during use of said cap that would result in cracking with concomitant leakage of electric current during use and breakage of wires.

Further in accordance with this invention is provided a method for the manufacture of an electric blasting cap which comprises disposing in a blasting cap shell a dielectric plug in waterproof sealed relation with the inner walls thereof and containing electrical conductor pins bridged in said shell in operative communication with a heat-sensitive material therein to transfer heat, when electrically heated, to said material; and extending said pins upwardly in said plug and terminating same in direct communication with the outside of said shell. Still in accordance with this invention a method is provided for the manufacture of a finished electric blasting cap which comprises disposing in a blasting cap shell a dielectric plug in waterproof sealed relation with the inner walls thereof and containing electrical conductor pins bridged in said shell in operative communication with a heat-sensitive material therein to transfer heat, when electrically heated, to said material; extending said pins upwardly in said plug and terminating same in direct communication with the outside of said shell; thereafter securing a lead wire outside said shell in electrically conductive contact with each said pin and then sealing a dielectric material around each connected lead wire-pin pair and between each said pair in contact with said cap, said dielectric material being capable of effecting a seal with each said leg wire-pin pair to insulate each said pair of wires from the other and from moisture, and being of suflicient strength to withstand failure during use of said cap that would result in cracking with concomitant leakage of electric current during use, and breakage of wires.

In a preferred embodiment of our invention a pair of electrical conductor pins is disposed through a dielectric plug of plastic material, e.g., a Bakelite (phenolic resin) plug so that they extend from each end of the plug. We prefer to form the plug-pin assembly by molding the wire around the pins. The pins are connected on one side of the plug by a resistance or bridge wire, and the resulting assembly is inserted, bridge wire first, into a cap shell of metal or plastic adapted to receive the plug in tight waterproof sealed relation. A heat-sensitive material, generally an ignition or delay powder in operative contact with a base charge to cause detonation of same, is disposed in the shell below the plug in contact with the bridge wire to receive heat from the wire when the wire is electrically heated. The pins are extended upwardly from the plug in the shell and are terminated at a point in close proximity to the end of the said shell, which as illustrated with reference to the drawings can be inside or outside the shell. The unit thus completed can be tested, stored, shipped or otherwise handled prior to its intended use in the field without there being a possible accidental firing as would be the case with such a cap when connected with a wire bundle. Also, the unit is hermetically sealed and will not deteriorate on storage. Subsequent to such handling and, if desired, just prior to actual use, lead wires are secured in physical contact with the pins to form respective lead wire-pin pairs, preferably by mechanical lock, as by a sleeve-type connector. This removes any need for heat treatment such as during welding or soldering. A plastic dielectric material, capable of maintaining a plastic-Wire moistureproof seal at the point of juncture and of forming a seal with the cap shell and further being of sulficient strength to withstand failure, e.g., cracks or breakage that would occur during use of the cap, is applied by any suitable method to the wire junctures and cap. Preferably, this is done by injection molding or thermosetting a resin around the wire pairs and cap. The plastic is disposed between the wire pairs and around them, in contact with the cap shell. The finished cap, including lead wires connected to the pins, is in condition for firing under any conditions, including those encountered when exposed to high heads of water in a borehole. It has heretofore been necessary to attach the lead wires to the pins and seal the joint in the plug at the time of making the cap or extend the lead wires in lieu of pins through the plug to the bridge wire in order to be certain that a waterproof connection of lead wires to bridge wire would be obtained. That, of course, has made it necessary to complete the entire cap unit at the time of its manufacture, with inherent hazards during storage and other handling, that have been eliminated by this invention.

Any dielectric material is a suitable seal material for use in the practice of this invention that (1) can form a moistureproof seal with the lead wires and pins at their point of juncture and adjacent bared portions, (2) can adhere to or form a seal with the cap shell and ignition plug, (3) is of sulficient strength that it will not crack, break or otherwise mechanically fail during life of the cap, e.g., under storage conditions, shipping and other handling, and actual disposition and use in the borehole. The seal can be applied by any suitable method, preferably by injection molding or simple molding with a thermosetting resin. We have found polyethylene of softening point of 100 C. and higher, and thermoplastic ethyl cellulose (at least two ethoxy groups per anhydroglucose unit) especially adaptable to the injection molding procedure. Ordinarily, these seals are formed in a simple split mold machine, although any suitable mold or injection machine can be employed.

The seal preferably has about the same base diameter as that of the cap, tapering somewhat toward its end away from the cap shell. Any suitable length seal can be employed, although a seal extending in the order of from about A to /2 inch along the wires outside the shell is generally utilized. Thus, the configuration of the seal is one largely of choice.

The following examples are illustrative of formation of dielectric seals in accordance with the invention.

Example 1 Thermoplastic ethyl cellulose was injection molded around a mechanically locked lead wire-pin jointure of an electric blasting cap of this invention. The formulation was, on a weight basis, parts of ethyl cellulose having from about 45.5 to 46.8 ethoxyl groups per anhydroglucose group and having a viscosity of about 70 centipoises as measured as a 5 percent solution in 8020 toluene-ethanol at 25 C., about 10 parts of Dow Resin V-2 (a trimer of a-methyl styrene), and about 5 parts of Santicizer 16 which is butyl phthalyl butyl glycolate. A minor amount of diamyl phenol stabilizer was present.

Example 2 A somewhat softer formulation than that of Example 1 was employed in injection molding of a seal around a lead wire-pin jointure of Example 1, namely, parts of ethyl cellulose having from about 45.5 to 46.8 ethoxyl groups per anhydroglucose group and a viscosity of about 100 centipoises as measured as a 5 percent solution in 8020 toluene-ethanol at 25 C., 23 parts of tri-2-ethylhexyl phosphate as plasticizer, and 2 parts diamyl phenol.

Example 3 A seal of clear grade polyethylene of softening point of about 212 F. was injection molded around a lead wire-pin jointure and cap shell of Example 1.

In each of the three preceding examples the seal was waterproof, of strength to withstand failure by cracking, breaking or the like, and was not in any way deteriorated at F. storage. The cylinder temperatures ranged from 320-380 F., during the foregoing injection moldings.

In each injection molding procedure a Plasticor molding machine was employed. This mold consists of a cavity which grips the lower section of the cap shell, the cavity having a constriction to hold the cap shell at the point where it is enlarged by insertion of the ignition plug, generally a molded Bakelite (phenol-formaldehyde) plug. Two narrow circular holes are provided in the mold to hold the leg wires so that when the cap is placed in the mold, there is a closed cavity between the end of the mold and the upper end of the cap, and it is in this cavity that the seal material is molded. The mold is provided with guide pins to maintain its alignment. Obviously, other molding machines and methods can be employed.

In operation of each of Examples l-3, the mold was readily filled, giving a complete sealed closure of the cap and a well-formed seal, insulating the bare wire pairs from moisture and electric charges.

We have found that thermosetting resins, as well as thermoplastic resins, can advantageously be employed in making the nonconductor seals of this invention. Thus, any fluid thermosetting resin can be poured into a cup mold around the top of the blasting cap and the leg wirelead wire juncture. It is preferred that the cure time of the sealing material be sufiiciently short inasmuch as if it is too long, an unduly large number of molds are required in a continuous manufacturing process. Accordingly, the preferred setting time does not exceed about 5 minutes at room temperature, although longer curing times can be employed, e.g., 30 minutes at 60 C. Curing times may be any suitable duration e.g., up to 45 minutes or longer, although shorter curing times are obviously most advantageous.

A preferred thermosetting resin material is Stypol 705, a styrene-polyester modified with vinyl toluene to regulate fluidity and catalyzed with benzoyl peroxide. A promoter is generally employed when molding Stypol 705 at room temperature, cobalt naphthenate containing about 6 percent cobalt being exemplary of a suitable promoter.

Such a system gels, or sets, sufiiciently to be removed from the mold in 2-3 minutes at room temperature and becomes completely cured and hard in 15 20 minutes at room temperature.

Thermosetting resins of short cure time can be treated in various manners to overcome unduly short pot life. Thus, in the above Stypol system, the promoter is dissolved in the resin, the latter having a long pot life, and the catalyst is dissolved in a separate resin portion and the two solutions are mixed just prior to molding. Such mixing can be carried out by way of impinging jets of each solution on the other directly in the mold. Inasmuch as both promoter and catalyst solutions are stable in themselves at room temperature, no gelation occurs except in the mold. Any suitable manner of impinging the separate streams can be utilized.

When referring herein to cure time, it is meant the time required for complete cure or hardening of the resin whereas by set time is meant the time required for sufiicient gelation or partial cure to take place such that the resin can be removed from the mold for completion of cure. By the term pot life it is meant the time during which the ingredients are in admixture without set taking place, i.e., prior to the actual step of molding.

Cellosolve acetate, ethylene dichloride and acetone are suitable solvents for the uncured resin system.

The following examples are illustrative of seals of this invention made from thermosetting resins.

Example 4 Two solutions of a thermosetting resin were prepared. Solution A was prepared by mixing, on a weight basis, 80 parts of Stypol 705, 19 parts vinyltoluene and 1 part cobalt naphthenate. Solution B was prepared by dissolving 6 parts of benzoyl peroxide in 20 parts of styrene. Twenty-four parts of Solution B were then mixed with 74 parts of Solution A to form Solution C. Solution D was prepared by dissolving 2 /2 parts of Naugatuck promoter No. 2 in 97 /2 parts of Solution A. Solutions C and D were then introduced as separate impinging jet streams into a cup mold around a leg wire-lead wire juncture and shell top of an electric blasting cap in equal parts by weight to obtain a seal of this invention.

Example 5 A seal was made in accordance with the procedure of Example 4, the final seal composition being 82.5 percent Stypol 107, 1.75 percent benzoyl peroxide, 0.75 percent Naugatuck promoter No. 2, and 15 percent styrene. This resin was somewhat less fluid than that of Example 4. At room temperature gel time was 3 minutes and hardening time was 15 minutes. The resulting cap was immersed in salt water for 6 days at 200 p.s.i., the lowest resistance between unbridged leg wires being 30,000 ohms and between leg wire and copper shell being 28,000 ohms.

Example 6 Araldite CN504, an ethoxylene-type resin (condensation products of polyaryl ethylene oxides with acid anhydrides and amines), was mixed at room temperature with about 15 percent of its weight of diethylene triamine. The resulting mixture was poured into a mold disposed around wire junctures and cap shell top as described in Example 4. The mixture had appreciable pot life at room temperature and cured in about 15 minutes at 60 C.

Seals made in accordance with the foregoing Examples 4-6 do not show deterioration upon hot storage over prolonged periods, and exhibit requisite physical strength for withstanding failure such as by cracks or breaks and provide requisite electric and moisture insulation for the bared Wire portions. Thus, the seals of Examples 4 and 5 were not adversely affected by several months of hot storage and would not crack at --30 C.

Exemplary of other thermosetting resin seal materials of our invention are (l) Narmco 3117 (a polyester resin) benzoyl peroxide Naugatuck promoter No. 2 styrene in respective weight percent proportions of 87.8, 1.5, 0.7 and 10, with a gel time of 3 minutes and a hardening time of 15 minutes, both at room temperature, (2) Stypol 107E/ cyclohexanonehydroperoxide/benzoyl peroxide Naugatuck promoter No. 2/ styrene in weight percent respective proportions of 87.2, 0.5, 1.5, 0.8 and 10 with a gel time of 4 minutes and a hardening time of 15 minutes, both at room temperature, and (3) Stypol l07E/benzoyl peroxide promoter No. Z/Lupersol DDM (60 percent solution of methylethylketoneperoxide in dimethylphthalate) styrene in respective weight proportions of 87.8, 1.0, 0.7, 0.5 and 10, with a gel time of 10 minutes and a hardening time less than 30 minutes, both at room temperature. Hydroxyheptyl peroxide is also advantageously utilized as the peroxide component.

The invention is further illustrated with reference to the drawings. Fig. 1 is illustrative of a fully assembled unit cap of this invention. Fig. 2 illustrates the unit of Fig. 1 connected with a conventional Wire bundle, such as subsequent to storage and other requisite handling. Fig. 3 illustrates a dielectric seal material of this invention and its application to a specially shaped cap to bond the wires and to adhere to, or bond, the shell as the case may be. Fig. 4 illustrates a plastic-type shell disposed around a metal cap shell and which can be directly sealed with the leg wires and pins to form a seal of this invention. Fig. 5 further illustrates a plastic covered metal shell of Fig. 4, Fig. 6 illustrating strips of sealing material that can be utilized in making the cap of Fig. 5. Fig. 7 shows ears formed, as a result of employing strips of sealing material heat-sealed to form the plastic shell such as of Figs. 4 and 5. Fig. 8 shows a completed unit in which the sealing material comprises a plurality of strips surrounding the shell and disposed in sealed relationship with the leg wires When the latter are sealed to the cap pins. Fig. 9 illustrates an embodiment employing use of a sleeve member, metal, plastic or paper, in imparting additional strength to the seal. Figs. 10 and 11 illustrate an embodiment employing a specific saw-tooth type interlock ing of wires and pin with termination of the pins inside the shell. Figs. 12a, 12b and further illustrate a method for making a blasting cap assembly of this invention. Figs. 13a and 13b illustrate a unit cap wherein the ignition plug terminates short of the shell end to form a cavity in which all or a portion of the dielectric seal can be disposed. Fig. 14 illustrates a cavity in the top of the ignition plug in which seal material can be disposed.

With reference to Fig. 1, cap unit 1 constitutes blasting cap shell 2, metal or plastic, containing pins 3 terminating outside shell 2 and bridge wire 4 across pins 3, the bridge wire being in contact with any suitable heat-sensitive material 5 such as an admixture of mercury fulminate and potassium chlorate, diazodinitrophenol and potassium chlorate, nitromannite, lead styphnate, lead azide or the like. Heat-sensitive material 5, although shown as a loose mixture can, if desired, be in head, pressed or buttered form. Base change 5a in the bottom and closed end of shell 2 is any suitable material detonatable by heat from ignition of mixture 5 or by detonation of a primer (not shown) disposed intermediate the base charge 5a and ignition mixture 5, and detonatable by heat from ignition of mixture 5.

Illustrative of suitable base charges are pentaerythritol tetranitrate, tetryl, nitrostarch, cyclonite (cyclotrimethylene trinitramine), mannitol hexanitrate and the like. Illustrative of suitable primer compositions are diazodinitrophenol, lead styphnate, lead azide and mercury fulminate, these compounds also being capable of functioning as ignition compounds in the absence of a primer, as is well known in the art.

Ignition plug 6 is disposed in the top and open end of shell 1 and contains pins 3 extending through it from bridge wire 4 and terminating in close proximity to the outside of the shell at 7. Ignition plug 6 is assembled in sealed watertight relationship with the interior walls of shell 2. Ordinarily, a watertight joint is obtained by making the outside diameter of the plug slightly larger than the inside diameter of the shell and pressing the plug into the shell. This causes the shell to expand or bulge and to frictionally hold the plug in a tight grip. Insertion may be facilitated by slightly tapering the entrance end of the plug or by slightly flaring the open end of the shell. A wax layer on the outer plug surface facilitates pressing the plug into the shell and provides an improved watertight fit.

This unit is free from the wire bundle, i.e., leg wires, and can be handled, stored and otherwise moved as desired without the hazards ordinarily present when wire bundles are attached. The unit eliminates the undue bulk and weight characteristic of the prior art caps assembled with leg wire bundle during manufacture, and provides thereby for greatly simplified handling up to the time of use. Also, the cap unit provides for a choice of type of lead wires at a time after assembly of the cap, such as at the time of use.

Any suitable plug material can be employed. Thermosetting resin materials such as rubber, alkyd resins, phenol-formaldehyde resins, urea-formaldehyde resins and sulfonamide resins are examplary. Bakelite is a now preferred material. Although thermoplastic resins, in some instances, show a tendency toward cold flow, thermoplastic resins such as those of polystyrene, vinylidine chloride, cellulose acetate butyrate, polyamides, vinyl chloride and vinyl acetate have been employed. Also, vinyl acetate-vinyl chloride rubber materials, and polyethylene have proved satisfactory.

Preferably a plug of moldable material is molded around the pins 3, to form the plug-pin assembly. Thus, either a stiff or soft pin can be employed. However, if desired, the pins, if sufiiciently stiff, can be inserted in and through the plug by hand or by mechanical means. Exemplary pin materials are iron, steel, copper, nickel, nickel-silver, silver and Invar.

The initiator shell 2 is either metal or plastic. By way of example, it may be made from any desirable copper alloy, aluminum, bronze or similar ductile metalilc material or from any suitable plastic material such as thermosetting molding compositions based on resins of the phenol-formaldehyde, casein-formaldehyde, ureaformaldehyde, and phenol-furfural types, and thermoplastic molding compositions formulated from cellulose esters, cellulose ethers, polymerized esters of acrylic and substituted acrylic acids, polystyrene, chlorinated rubber, modified isomerized rubber, vinyl chloride, vinyl acetate polyethylene and the like.

Fig. 2 illustrated the wire bundle 8, i.e., insulated lead wires 9 with bared portions 9a connected with bare pins 3 at 7a. Attachment at this point is preferably by mechanical locking, e.g., by a crimped sleeve connector; it being an advantageous feature of this invention that heat treatment of any kind need not be employed in connecting the leg wires and pins. Although soldering can be employed with quite some degree of safety, we prefer to effect jointure by mechanical locking to assure maximum safety. However, welding or soldering can be utilized if desired.

With reference to the embodiment of Fig. 3, a plastic seal material 11 of this invention surrounds the bared portions of wire bundle 8 and pins 3 connected at 711., making a bond to the bared wires and also to the shell 2. A true bond between the sealing material 11 and the cap shell and/ or ignition plug is not essential, provided there will be no separation or failure at such points. Shell 2 as at 12 and 12a is particularly advantageously employed without such a bond of shell and seal material. Thus, the top or neck portion 12a of Fig. 3 extends into the seal body 11 in a manner to lend support to the body 11 in lieu of support recived from a true bond. However, we prefer a true bond between seal material and cap and/or ignition plug in order to assure against all current leakages even though small leakages can be tolerated.

When the cap shell 2 is of material similar in heatsealing properties to the sealing material, then the materials may be made to blend together and provide a true seal so that the bared Wires and pins, the seal material and the shell form a unitary mass. This can be done without adversely affecting the cap itself in any manner, and provides for added strength of the dielectric seal 11.

With reference to Fig. 4, an open end shell 11a of plastice seal material of this invention is molded so as to accept a unit cap (Fig. 1) with pins 3 terminating in the open end 12 of the shell, and so that insulated wire portions 9 when attached at 7a to pins 3 will also be within the open end 12. As illustrated with reference to Fig. 5, the open end 12 is then pressed down under pressure, and heat is locally applied to cause the bared wires and shell to form a seal of this invention. This seal, when desired, can function as a waterproof seal for the entire cap unit. It is advantageous in accordance with this embodiment to add an extra portion of sealing material between the lead wire-pin pairs prior to making the final seal so as to provide added protection against shorting across the lead-pin junctures inside the plastic shell.

Figs. 6 and 7 illustrate another embodiment involving an over-all plastic coating of the metallic shell and the Wire junctures. A strip 11b of thermoplastic seal material of this invention is formed on each side of the metal shell as one illustrated with reference to Fig. 7. The final structure is shown with reference to Fig. 8 in which the two strips 11b are sealed along the lines 14 all around the edge of the metallic cap 2, forming a point structure at 16 and a seal of Fig. 5 around the insulated wires 9, thereby covering all points of the metal shell unit including the projecting pins and the bared lead wires. The ears at 14 which are formed by the closing together of the strips of material as illustrated in Fig. 7 may be sheared off.

The plastic covering illustrated (11a, Figs. 4, 5 and 11b, Figs. 6, 7, 8) provides corrosion protection for the metallic shell 2 and through its insulating property also provides protection against stray currents. The plastic covering of this embodiment can be of appropriate warning color such as bright red, orange, yellow, white, etc., and can also be stamped or marked with such words as Explosives Dangerous or any other such warnings.

The embodiments of Figs. 4-8 provide a still further advantage, namely, that molding of the plastic seal material around the entire finished assembly is eliminated and only such seams as seams 14 of Fig. 7 need be heated. Although such an overall molding operation can be carried out, it is inadvisable inasmuch as the heat content of the plastic covering material can be of sufiicient magnitude, during molding, that heat-flow into the cap 2 from the plastic tube during molding might cause the explosive inside the shell to reach temperatures that are not adequately safe. In accordance with the embodiments of Figs. 4-8, the amount of heat required for closing the thermoplastic envelope is a minimum and will under no circumstances cause development of unsafe temperatures in the explosive.

In another embodiment, Fig. 9, the bared leg wires 3 extending from cap shell 2 and terminating at 7a are connected with the bared lead wires 9a of bundle 8 and then a supporting sleeve 10, such as of metal, plastic or paper, is formed on the cap end encompassing the bared wire portions and extending to the covered lead wire 9. Seal material is then poured or injected into the form in contact with the shell and insulated lead wire to form the solid plastic seal. The sleeve can lend additional support to the seal dependent upon the seal material selected which will be particularly advantageous in that the seal material can be selected from a broader strength range of materials. The sleeve 10 permits setting up of a seal over longer periods than otherwise considered practicable for forming the seal from a thermosetting resin. The sleeve in effect serves as an expendable unit mold.

With reference to Figs. 10 and 11 is shown an additional embodiment of mechanical locking that can be employed in the practice of our invention. Thus,pins 3 are sawtoothed and are terminated within cavity 6a of plug 6 in the cap shell so as to accept bared leads 9a of wire bundle 8, also saw-toothed, in locked relationship all within the upper portion 6a of plug 6. A thermoset plastic seal material of this invention is then poured into the cavity portion 6a to cure and set around the wire-pin connection 7a and an insulated wire portion 9. This embodiment, as that of Fig. 9, provides for a selection from a broader strength range of seal materials, inasmuch as the seal material supported by the plug cavity can be gelled away from the molding operation and a longer gelling time becomes more practicable. It is advantageous in this embodiment to select a resin that will cure and set at about 150 C. or lower, preferably at about room temperature, such as the composition of Example 5. However, if cooling is employed, higher curing temperatures can be employed. The seal material is advantageously extended to above the shell to impart added strength to the overall seal, and in that event the saw-toothed portions can be in the plug or above it, as desired. However, to the extent that there is no sleeve support for the extended seal material, set times somewhat shorter than those employed with the sleeve will be more practicable from the manufacturing standpoint. Fig. 11 illustrates the plastic seal and saw-toothed connection in place.

With reference to Figs. 12a, 12b and 120 is further illustrated our now preferred method embodiment. A cap shell 2 formed from any suitable material such as above described, generally a copper alloy, is formed with closed end 22 and open end 21 and charged with a base charge a and a heat-sensitive material 5. A dielectric plug 6, generally a phenolic resin material, is molded around pins 3, and bridge wire 4 is welded or soldered across pins 3 as shown in Fig. 12b. The plug assembly of Fig. 12b is then wax-coated and inserted into the open shell end 21 to form a tight waterproof fit with the inner wall of shell 2. The distance from plug 6 to bridge wire 4 is such that when the resulting plug assembly is inserted, bridge wire first, in cap 2, the bridge wire when heated will be in operative contact with the heat-sensitive material 5 to transfer heat to it to cause ignition of same. Pins 3 of unit 25 are extended from plug 6 to a point 7a in close proximity to the outside of shell 2. That can be done by terminating the extended pins either before or after insertion of unit 25 in shell 2.

Insulated leg wires 9 of wire bundle are bared at 9a and mechanically locked with pins 3 at 7a, such as by a crimped sleeve connector to form separate legwire-pin pairs a and 1; connecting with bridge wire 4.

A plastic seal material 26 of this invention, ethyl cellulose and polyethylene being now preferred materials, is then injection molded, as with a Plasticor machine described hereinabove, around and between each leg wirepin pair a and b and in contact with cap shell 2 and insulated wires 9, to form a leg wire-pin shell seal of this invention.

It is understood that all dielectric seals of this invention encompass the bare pins and bared leg wire portions and a portion of the leg wire insulation and, in most instances, a portion of the cap. shell. In those instances wherein the dielectric seals do not contact the shell, they directly contact the plug 6. All seals are moisture resistant and exhibit the characteristics set forth herein. When referring herein to termination of pin wires in direct communication with the outside of the cap shell, it is meant that there is no intervening agency between the terminated pin ends and the outside of the shell so that leg wires outside the shell can always be directly connected with the pins as 10 by soldering or by mechanical lock as with a locking sleeve connector. Thus, whether the pins are terminated inside or outside the plug, they are always in direct communication with the outside of thecap shell and can be directly connected with leg wires.

The. pins are terminated at points within the shell or outside as illustrated. However, in any event, they do not extend outside the shell beyond points in close proximity to the shell end. Such distance, as will be appreciated, is variable dependent upon the size of each cap pin and leg wire and the manner in which the leg wires are to be connected with the pins. By way of example, a suitable connection of pin with leg wire can generally be made in any event when pins extend above the shell, say from Va to 2 inches. However, in some instances, it may be desirable to extend the pins a somewhat greater distance, such as when employing a plastic outer shell as illustrated with reference to Figs. 4 and 5.

With reference to Figs. 13a and 13b, a unit cap such as of Fig. 1 contains ignition plug 6 terminated short of the top shell end so that after the shell end is crimped, there will be a cavity formed into which the dielectric seal material can be inserted. Although the seal material in the cavity is sufiicient in the practice of this invention when the leg wire-pin jointures and insulated wire portions 9 are in the cavity, it can in any event form a part of an overall body of seal material extending above the shell end along the leg wires as shown with reference to Fig. 13b to provide a locking action on the seal above the shell to further strengthen the over-all seal.

Although generally the seal material will be placed in direct contact with the metal or plastic shell wall, it can if desired be disposed in contact with the ignition plug only. Thus, in some instances, the plug may extend outside the shell and the seal disposed in direct contact with the plug material and out of contact with the shell. Preferably, the ignition plug is placed about flush with the shell top end and the pins extend as stubs a short distance above or away from the plug. Upon connecting the leg wires and pins, the dielectric seal material, in most instances a plastic material, can be applied and contacted with the cap shell. However, as above discussed, the seal material can be contacted with the plug only, if desired.

As illustrated with reference to Figure 14 a cavity 6b in plug 6 can be provided for accepting additional seal material in support of the leg wire-pin seal. Cavity 6b can be utilized with or Without the additional cavity of Figure 1 (also shown in Figure 13a) intermediate plug 6 and the top end of shell 2.

When referring herein to bridge wire structure conmeeting or bridging conductor pins inside the cap, it is meant to include ignition assemblies wherein the bridge wire bridges the pins through conductors extended from the pins, e.g., bridge wires in a matchhead assembly connected with the pins to conductors extended from the ends of the pins.

As will be evident to those skilled in the art, various modifications can be made or followed in light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim and desire to protect by Letters Patent 1s:

1. In an electric blasting cap assembly comprising an elongated shell closed at one end and open at the other end, and having water impervious walls, an ignition plug within said shell in transverse water-tight closing relation therewith, a heat-sensitive composition in said shell between said ignition plug and said closed end; a pair of conductor wires extending into said shell through the said open end and through said ignition plug, and a bridge wire connected across the terminating ends of said conductor wires in operative communication with said heat-sensitive composition to cause actuation of same by transfer of heat upon passage of electric current through said conductors and said bridge wire, the improvement comprising said ignition plug disposed within said shell intermediate the said shell ends to divide said shell into an enclosed portion and an open end cavity portion; said shell being crimped at its open end to form a lip directed inwardly toward the shell axis, said conductor wires extending from said bridge wire through said plug and said cavity to the outside of said shell and terminating adjacent the said open shell end and lip; a separate lead wire outside said shell secured to each said conductor wire at the end thereof terminated as above described; a plastic dielectric material, as a unitary mass, filling said cavity and abutted therein against the shell well, said ignition plug, and the inner wall of said lip, and extending from said cavity around and between each connected pair of lead-conductor wires in sealed relationship with each said connected pair of lead-conductor wires and the walls of said shell and said lip to insulate each said pair from each other and from moisture.

2. An assembly of claim 1 wherein a cavity is also disposed in the top end of said ignition plug and a portion of said dielectric material is placed in the last said cavity.

3. A blasting cap assembly of claim 1 wherein said dielectric material is ethyl cellulose.

4. A blasting cap assembly of claim 1 wherein said dielectric material is a polyethylene having a softening point about 100 C.

5. A blasting cap assembly of claim 1 wherein said dielectric material is a styrene polyester.

6. A blasting cap assembly of claim 1 wherein said dielectric material is an ethoxylene-type resin.

7. In the manufacture of an electric blasting cap wherein a dielectric plug containing conductor wires extending therethrough is sealed within an elongated cap shell containing an open end and a closed end in transverse water-tight closed relationship therewith, and wherein said conductor wires are bridged within said shell in operative relationship with a heat-sensitive material to transfer heat to said material when electrically heated, and wherein said conductor wires are extended from their bridged ends through said plug to the outside of said shell a sufficient distance for connecting with an electric power source remote from said shell, the improvement comprising forming an assembly comprising said ignition plug with said conductors extending therethrough and connected on one side of said plug with a bridge wire, and terminating the ends of said conductors opposite said bridged ends to extend from said plug as described hereinafter; inserting the resulting ignition plug assembly, bridge wire first, through the open end of said shell into said shell and in said transverse water-tight closing relationship therewith, a distance sufficient to divide said shell into an enclosed portion containing said bridge wire and an open end cavity portion and to extend the said terminated ends of said conductors through said cavity and said open shell end to the outside of said shell adjacent the said open end; crimping the said open end of said shell to form an inwardly extending lip toward the shell axis; connecting a separate lead wire outside said shell with each conductor wire at its end terminated as above described; and then sealing each said pair of connected wires from each other and from moisture by filling the said cavity with a plastic dielectric material, as a unitary mass, so as to abut said material against said ignition plug and the inner walls of said shell and lip and then extending said mass from said cavity around and between each said connected pair of conductor-lead Wires to insulate each said pair from the other and from moisture.

8. A blasting cap assembly comprising an elongated blasting cap shell having an open end and a closed end; a heat-sensitive material in said shell; an ignition plug in said shell in water-proof sealed relation with the posed in, and extending through, said shell; a bridge wire connecting said pins in said shell and in operative communication with said heat-sensitive material to transfer heat to same when electrically heated, said shell being crimped at its open end to form a lip directed inwardly toward the shell axis and said ignition plug abutting the resulting lipped inner shell wall, about its periphery, to retain the opening in said crimped end as an open cavity; said pins extending upwardly through said plug and terminating at a point in close proximity to the crimped end of said shell; a separate lead wire secured to each pin, and a plastic dielectric material sealed around each connected pair of lead-pin wires and between each said pair and extended into said cavity against said plug to insulate each said pair from the other and from moisture.

9. An assembly of claim 8 wherein each said pin extends from said ignition plug to a point outside said shell.

10. An assembly of claim 8 wherein said pins are terminated inside a centrally disposed cavity in the top end of said plug and are saw-toothed, wherein said lead wires are saw-toothed to engage said pins in said centrally disposed cavity, and wherein said plastic material is disposed in said centrally disposed cavity.

11. An assembly of claim 8 wherein the said pin wires extend through said plug to a point outside said shell, wherein a supporting sleeve is adapted to connect with said cap shell and encompass said lead wire-pin pairs at their point of juncture and wherein at least a portion of said dielectric material is disposed in said sleeve.

12. In an electric blasting cap assembly comprising an elongated shell closed at one end and open at the other end, an ignition plug within said shell in transverse watertight closing relation therewith, a heat-sensitive composition in said shell between said ignition plug and said closed end; a pair of conductor Wires extending into said shell through the said open end and through said ignition plug, and a bridge wire connected across the terminating ends of said conductor wire in operative communication with said heat-sensitive composition to cause actuation of same by transfer of heat upon passage of electric current through said conductors and said bridge wire, the improvement comprising said ignition plug disposed within said shell intermediate the said shell ends to divide said shell into an enclosed portion and an open end cavity portion; said shell being crimped at its open end to form a lip directed inwardly toward the shell axis, said conductor wires extending from said bridge wire through said ignition plug into and through at least a portion of said cavity to a point in close proximity to the lipped open end of said shell; a separate lead wire outside said shell secured to each said conductor wire at the end thereof terminated as above described; a plastic dielectric material, as a unitary mass, filling said cavity and abutted therein against the shell wall, said ignition plug, and the inner wall of said lip, and extending from said cavity around and between each connected pair of lead-conductor wires in sealed relationship with each said connected pair of lead-conductor wires and the inner wall of the lipped end of said shell to insulate each said pair from each other and from moisture.

13. In the manufacture of an electric blasting cap wherein a dielectric plug containing conductor wires extending therethrough is sealed within an elongated cap shell containing an open end and a closed end in transverse water-tight closed relationship therewith, and wherein said conductor wires are bridged within said shell in operative relationship with a heat-sensitive material to transfer heat to said material when electrically heated, and wherein said conductor wires are extended from their bridged ends through said plug toward the outside of interior walls of said shell; electrical conductor pins dissaid shell a sufiicient distance for connecting with an electric power source remote from said shell, the improvement comprising forming an assembly comprising said dielectric plug with said conductor wires extending therethrough and connected on one side of said dielectric plug with a bridge wire, and terminating the ends of said conductor wires opposite said bridged ends to extend from said ignition plug as described hereinafter; inserting the resulting assembly, bridge wire first, into said shell through the said open end thereof into said transverse water-tight closing relationship therewith, a distance sufficient to divide said shell into a closed end portion containing said bridge wire and an open end cavity portion and to extend the terminated end of each said conductor wire through at least a portion of said open end cavity to a point in close proximity to the open end of said shell; crimping the said open end of said shell to form an inwardly extending lip toward the shell axis; connecting a separate lead wire, from outside said shell, with each conductor wire at the end thereof in close proximity to said open shell end as described; and then sealing each said pair of connected wires from each other and from moisture by filling the said cavity with a plastic dielectric material, as a unitary mass, so as to abut said material against said dielectric plug and the inner walls of said cavity and then extending said mass from said cavity around and between each said connected pair of conductor-lead wires to insulate each said pair from the other and from moisture.

14. In a process of claim 13, forming said assembly by injection molding a dielectric plug around a pair of the said conductor wires and then connecting each said conductor wire with said bridge wire as described.

15. In a process of claim 13, inserting said plug assembly in said shell a distance such that when said shell is crimped, as described, the resulting lip can be pressed down upon said plug to retain an opening through the resulting crimped end as said cavity, and then so crimping the said shell open end onto said plug.

References Cited in the file of this patent UNITED STATES PATENTS 1 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,965,033

December 20, 1960 Charles F. Horne et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, charge exemplary read 4-- plastic read above about 100 C.

line 58, for "Base change" read Base column '7, line 25, for "exemplary" read lines 42 and 43, for "metalilc" read metallic line 52 for "illustrated" read M illustrates for "reclved" read received line 74,

column 8, line 12, for "plastics"; column 11, line 28, for "about 100 C."

Signed and sealed this 9th day of May 1961,

(SEAL) Attestz- ERNEST W, SWIDER Attesting Officer DAVID L, LADD Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No; 2,965,033 December 20 1960 Charles F, Horne et al.

Column 6 line 58, for "Base change" read Base charge column 7,, line 25 for '"examplary" read exemplary lines 42 and 43, for "metalilc" read metallic line 52, for "illustrated" read illustrates line 74, for "recived" read received column 8 line 12 for plastic read plastic column 11, line 28, for "about 100 C." read above about 100 C.

Signed and sealed this 9th day of May 1961.

(SEAL) Attestz- ERNEST W, -SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No; 2965 033 December 20 1960 Charles F. Home et a1.

Column 6 line 58 for "Base change" read Base charge column 7, line 25 for ""examplary" read exemplary lines 42 and 43, for "metalilc" read metallic line 52 for illustrated" read illustrates line 74, for "recived" read received column 8 line 12, for "plastic read plastic column ll line 28 for "about 100 C." read above about 100 C.

Signed and sealed this 9th day of May 1961 (SEAL) Attest:

ERNEST W, -SWIDER DAVID L-o LADD Attesting Officer Commissioner of Patents