US2515780A - Blasting cap manufacture - Google Patents

Description

July 18, 1950 E. K. LEFREN 2,515,780

BLASTING CAP MANUFACTURE Original Filed May 18, 1946 Patented July 18, 1950 BLASTIIYG CAP MANUFACTURE Edward x. lenen, Kingston, N. Y., minor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware original application May 1s, 194s, serial No.

670,795. Divided and this application November 13, 1947, Serial No. 785,769

11 Claims. (CL 86-1) l This invention relates to electric blasting initiators and more particularly to a novel and improved method for the manufacture of waterproof electric blasting initiators.

It is anobject of the present invention to provide an improved method of manufacturing an electric blasting initiator whereby the foregoing disadvantages are obviated. It is a further ob- According to one method of manufacturing 5 ject of the invention to provide an improved electric blasting initiators, the leg wires are emmethod for manufacturing electric blasting initibedded in a hard cast plug of sulfur which is then ators which is faster, more economical and less inserted into the open end of a charged shell complicated than prior methods and which reand sealed by a heated mixture poured in behind sults in an improved electric initiator having het.. it. Such a method is subject to several disadter water-resistant properties, greater strength vantages. Considerable handling is required and greater resistance to the leg wires being acwhich is always disadvantageous in view of the cidentally pulled out. It is a still further object sensitive nature of the explosives employed. Also, of the invention to construct the ignition plug unless considerable care and skill are exercised assembly without softening or otherwise adversely when introducing the waterproofing compound. l5 affecting the leg Wires or the insulation thereon. it is quite likely that some of it will enter the Another object of the invention is to provide an explosive charge with deleterious effects. Moreignition plug which may be assembled in waterover, a relatively large amount of the sealing proof relation with the initiator shell without the compound is required to protect the cap against use of interior sealing compounds. These and moisture when stored under adverse conditions. other objects will be apparent as the description Thus, a longer initiator shell is required. Furproceeds. l thermore, this method is complicated, time con It has been found that the foregoing objects suming and expensive and does not always give are accomplished and the disadvantages overa closure which will retain its waterprooiness come by the method of this invention which comunder adverse conditions. prises forming a plug of dielectric material with- Another method, of more recent origin, comout leg wires, extending a pair of pins through prises molding and compressing a heated matcthe plug. attaching a pair of leg wires to one end rial about the leg wires of the electric blasting of the pins, advancing the'pins to move the coninitiator to form a plug, inserting the plug in the nections thus formed within the plug, ailxing a. shell and crimping the shell into the plugto form o bridge wire to the other end ofthe pins, and the seal. This method has many advantages but inserting the completed ignition plug into an iniis subject to the disadvantage that the operation tiator shell. of molding the material around the leg wires is In accordance with this invention, the plug is complicated, costly and time consuming and is deSirehly vmolded by heet and Pressure into the likely to result in an inferior product. In this desired Shape and size. Openings, extending operation, the temperatures utilized are sumthrough the plusy are provided adjacent One end cient-,1y great to cause softening 0f the insulation thereof in communication with a recess provided material of the wires and a consequent interat the Opposite ehd- The Pins are inserted mingling of this material with the thermoplastic through the Openings and the recess so that the plug material. The result is undesirable from the 4o ends 0f the pins protrude from the end of the standpoint of eliective molding and adversely af- Plllg- Les Wires are then soldered, welded or fects the strength, durability and appearance of otherwise attached to the pins', an insulating and the product. There is moreover a tendency to sealing compound introduced into the recess, and weaken the insulation adjacent to but exterior the pins pulled partly through the plug to move of the plug with the result that it soon cracks the bare ends of the wires into the insulating and and exposes the bare wires, thus increasing the sealing compound contained in the recess. The possibility of short circuits and other failures. Sealing Compound is then hardened t0 produce Attempts to overcome this result in further coma rigid, watertight connection. The pins are anplication and increased cost of the process. hOred against a pulling force on the leg Wires Additionally, in this type of operation, it isnecby ears or nicks made in the pins adjacent the essary to handle relatively long lengths of leg plug. The pins are then cut off a predetermined wire and to maintain the ends thereof in iixed distance from the end of the plug and the bridge positions during the molding operation. This is Wire aiiixed by soldering or welding. The comdiicult and exacting and represents another displeted ignition plus iS then assembled With the advantage inherent in such procedure. initiator shell in watertight relationship.

Having now described the invention in general terms, there follows a more detailed description of preferred embodiments thereof with reference to the accompanying drawings in which: Fig. 1

is a transverse cross-sectional view of the plug;

Fig. 2 is a transverse cross-sectional view of the plug showing the pins in place; Fig. 3 is a transverse cross-sectional view of the plug showing the pins in place and the leg wires attached thereto; Fig. 4 is a view similar to Fig. 3 showing the sealing compound in the recess; Fig. 5 is a View similar to Fig. v4 showing the pins yand wires moved to embed the bare ends of the leg wires in the sealing material; Fig. 6 is a view similar vto Fig. 5 showing the pins after they have been eared or nicked; Fig. 7 is a similar view showing the pins after they have been cut oil; Fig. 8 shows the addition of the bridge wire to form the completed ignition plug assembly; Fig. 9 is a transverse cross-sectional view of the assembled initiator; Fig. 10 is a view similar to Fig. 9 but shows g the end of the shell clamped down over the end of the plug; Fig. 11 is a transverse sectional v iew of a modiiied plug with the pins in position; and Fig. 12 is a transverse cross-sectional view of a modiiied type of initiator.

Referring now to the drawings, Figs. 1 through 10 illustrate the various stages of construction involved in the manufacture of a blasting initiator according to a preferred embodiment of this invention.

Fig. 1 shows the molded plug I0 having a recess II at one end and openings I2 and I3 extending inwardly from the opposite end; A taper I4 at one end of the plug permits easy insertion into the initiator shell and a sharper taper I5 at the opposite end of the plug provides a locking surface for engaging with the bent-over end portion ofthe shell to aid in keeping the assembly locked together.

Fig. 2 shows the plug I0 with the pins I6 and I1 in place. The pins are inserted through the openings I2 and I3, and the recess II. The pins may be suitably tapered to permit easy entry and passage through the plug.

Fig. 3 shows theplug and pin assembly with the leg wires I8 and I9 soldered or welded to the ends of the pins. Beads 20 and 2I are formed at the pin and wire joint as a result of the soldering or welding operation, y

Figs. 4 and 5 illustrate the addition of the sealing compound 22 (Fig. 4) and the embedding of the bare ends of the leg wires therein (Fig. 5). The latter operation is accomplished by pulling the pins I8 and I'I through the plug in the direction of the arrow shown in Fig. 5. This draws the bare ends of the leg wires into the soft insulating and sealing compound 22 which is subsequently hardened to form a rigid waterproof connection between the wires and plug.

Fig. 6 illustrates the step of earing or nicking the pins I6 and I1 as shown by the ears 23 and 2l, respectively, and Fig, 7 illustrates the step of cutting off the pins I6 and I1 at a predetermined distance from the end of the plug after caring.

Fig. 8 illustrates the step of attaching the bridge Wire 25 to the pins I6 and I'I.

Fig. 9 shows the initiator shell 26 and ignition plug I0 assembled in watertight relationship. Ordinarily a waterproof 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 latter to expand or bulge as at 28 and to frictionally hold the plug in a tight grip.

Insertion may be facilitated by slightly tapering the entrance end of the plug; as at Il, or by slightly flaring the open end of the shell.

Fig. 10 shows the completed initiator with the end of the shell folded around the end of the plug as at 29 to act as an additional means for holding the assembly in tight relationship.

The completed initiator resembles the normal device of this type except that it is considerably shorter and has the slight bulge heretofore mentioned which is hardly perceptible to the naked eye. The bulge will not normally increase the shell diameter more than about 0.003 inch but may be as much as`0.04 inch depending on the shell characteristicsand the plug diameter.

The plugs, in accordance with the preferred form of this invention, are formed from a hard dielectric material such as the thermosetting or thermoplastic resins. The material selected should be of suiiicient hardness to expand the shell and produce the bulge heretofore mentioned as well as highly resistant to cold flow.

The plugs will normally be cylindrical in shape, with a diameter from about 0.003 inch to about 0.005 inch greater than the inside diameter of the shell, and a length from about A inch to about inch.

The openings I2 and I3 are designed to facilitate entry and to insure correct spacing and alignment of the pins I6 and I1. They may be the same size as the pins but are preferably slightly smaller to insure a snug iit. They may extend completely through the plug or only partially therethrough. Depending upon the specific design of the mold, there may be a thin film of the plug material over one end of the openings. How- L', the pins are readily pushed through this The recess II is designed to receive the bare ends of the leg wires and to provide space for the introduction of a suitable amount of insulating and sealing compound. It should therefore have a suitable cross-sectional shape anddepth to accomplish these purposes. It has been found preferable to employ a. recess in which the cross-sectional shape is rectangular with rounded corners and the depth inthe order of about 1A, inch for a plug having a length of about 11g inch. However, other cros's-sectional shapes and other depths may be utilized with satisfactory results. In some cases, it may be desirable to provide separate recesses for each wire as shown at 32 and 33 in Fig. 1l. In other cases, the recess may be omitted with, however, probable adverse effect on the tightness, rigidity and waterproofness of the assembly when using a hard dielectric material for the plug. All such modifications and alternative forms of construction are within the purview. of this invention.

Plug materials suitable for use in the preferred form of this invention are required to have a compressive strength greater than the tensile strength of the shell. Plastic materials having a compressive strength above about 6,000 lbs/sq. inch, preferably between 16,000 and 40,000 lbs/sq. inch, a compression modulus of elasticity above l.3 lbs/sq. inch, preferably between 7.0 105 lbs./sq inch and 50 105 lbs/sq. inch, and coefficients of thermal expansion between about 2 l0-5 and 16 105 inches per inch per degree centigrade are preferred. Thermosetting resins, such as alkyd resins, phenol-formaldehyde resins, cresol-aldehyde resins, xylenol-aldehyde resins, urea-formaldehyde resins, phenol-furfural resins, thiourea-formaldehyde resins and sulfonamide resins, are satisfactory. Thermoplastic resins show a tendency toward cold ow and are, therefore. undesirable in some cases. However,

thermoplastic resins, such as aniline formaldehyde resins, polystyrene resins, vinylidene chloride resins, and hard ilow cellulose acetate butyrate resins have proved satisfactory. In accordance with a modified form of the invention, other materials may be used for the plug as will be pointed out hereinafter.

The pins i6 and l1 must be suiliciently stiff to permit passage through the plug without bending or breaking and also to resist bending or displacement in the subsequent operation of assemblmgethe plug and shell. Suitable materials for this purpose are iron, steel, copper, nickel, nickel silver. silver and invar. The diameter of the pins is preferably about 0.0005 inch larger than the inside diameter of the holes in the plugs, but may vary under some circumstances to a point wherein the hole in the plug is about 0.0002 inch larger than the wire diameter. It is preferred to use a wire diameter of 0.035 inch and a, plug hole diameter of 0.0345 irch. The length of the pins is determined by the length of the plug and is usually from about l inch to about 41 inch longer than the plug. The pins may be inserted in and through the plugs by hand or by mechanical means.

The leg wires which are used in the method of this invention are the normal wires used in the art. Thus, they may be copper wire, or iron wire, either plain or tinned. 'Ihey may be insulated in a desirable manner such as. for example, by using enamel, cotton servings. or plastic materials.

The leg wires are secured to the pins preferably by welding. This insures maximum strength and conductivity. Desirably a bead is formed at the welded joint to increase its effectiveness. Although welding is preferred, other. securing means, such as soldering, may be used.

In the preferred embodiment, the insulating and sealing compound 22 effectively insulates the bare end portions ofthe leg wires and forms a strong waterproof assembly of the pins and leg wires with the plug. Preferred materials for sealing should be hard and durable under all normal temperature conditions and capable of being* rendered soft or semiiluid for the initial application. Where a. molten sealing compound is used, the temperature will in all cases be insuicient to adversely aect the wire insulation thereon. The insulating and sealing compound, preferably a material which hardens by the addition of a setting-up agent or quick evaporation of solvents, may be introduced in any suitable manner either mechanically or by hand. Suitable materials for this'purpose are waxes, asphaltic materials, thermoplastic compounds or combinations of these. Other materials of a like nature may be used without departing from the scope of the invention.

The bare ends of theleg wires are pulled into the sealing compound while it is still molten and/or soft. This is accomplished by sliding the pins i6 and il through the plug I0 in the direction of the arrow shown in Fig. 5. This may be done manually or by suitable mechanical devices.

The ears 23 and 25 are made by slightly deforming the pins I6 and i1 adjacent the plug.

6 the pins I6 and l1 may be electrically resistant wire composed of noble or base metal, or alloys thereof. Thus, for example, platinum, Nlchrome, copper-nickel, or other alloys may be employed. The bridge wire is welded, soldered or otherwise secured adjacent the ends of the pins after they l have been cut off a predetermined distance from Care mustV be exercised to see that the pins are not substantially weakened thereby. The ears increase the pull-out resistance of the leg wires from the plug.

The bridge wire 25 used to connect the ends of the face ofthe plug.

In assembling the shell and plug, it has been found that the diameter of the plug and the shell provides the control for the waterproof seals. Best results are obtained when the plug has a diameter between about 0.003 inch and about 0.005 inch greater than the inside diameter of the shell. /Insertionis accomplished by means of a press.

In some cases, additional assurance of a waterproof seal, under extreme conditions, is obtained when a waxy material is utilized. 'I'he waxy material may be applied to the surface of the plug. or to the shell in the vicinity of the plug, or may be incorporated in the plug, or may be utilized in any combination of these. When the wax is incorporated in the plug material prior to molding an amount less than 5% by weight of the material, and preferably between about l/2% to about 3% is used. A combination of admixture and coating gives best results and is preferred where waterproofing under extremely high pressures is desired. Wax substances which have been found suitable include palm, ceresin, montan, stearin, beeswax, spermaceti, synthetic waxes and similar materials. In addition to contributing assurance of waterproofness, the presence of a wax also reduces the force required to insert the lar ductile metallic materials. The strength and thickness of the walls should be such that splitting does not occur when the oversized plug is forced thereinto. If desired, the upper portion of the shell may be constricted slightly before insertion of the plug and thus produce a shell with straight sides. However, production of the enlarged or expanded upper base portion type shell is preferred because of the ease of manufacture.

The explosive charge 21 is shown to consist of a single charge of material, but this explosive charge may be any of the normal explosive charges used in blasting caps. Thus, for example, it may consist of an admixture of mercury fulminate and potassium chlorate, or it may consist of a base charge of tetryl, nitro-starch, pentaerythritol tetranitrate, and the like, having superimposed thereon a charge consisting of an admixture of mercury fulminate and potassium chlorate, diazodinitrophenol and potassium chlorate, or lead azide and the like. The use of the various known explosive compositions and their arrangement within the cap are well known to the art and do not form part of the present invention.

In accordance with the preferred embodiment of this invention, the plugs may be formed by compression, transfer or injection molding methods. The compression and transfer methods of molding are preferred for the hard thermosetting resins; the injection molding method is preferred for the thermoplastics. These molding methods are likewise preferred when using resilient material wherein it is desired to provide the recess inthe plug.

When utilizing resilient material such as rubber, an extrusion method for forming the plugs may be used. In this embodiment of the invention, ythe resilient material is extruded in the form of a long strand having two apertures extending throughout its length. -The strand is thencut into units to form theindividual plugs.

The pins are inserted into the apertures of the individual plug units and the leg wires are aflixed to the pins. The connecting joint between the leg .wires and pins is then pulled into the apertures of the resilient material. With this method, the

recess is not necessary. lAlternatively, the resilient material may be extruded with two wires embedded therein and extending the length of the extruded strand. The strand is vthen cut into units to form individual plugs. The wires embedded therein serve as the pins. then compressed to expose the ends of the pins for ailixlng the leg wires thereto. The connection joint is ,then pulled or pushed into the resilient material thereby exposing Vthe other end of the pins. The bridge wire is then affixed to the exposed end of the pins.- With this method, the recess is likewise unnecessary. It is common practice to crimp the initiator shell into resilient plugs of this type. Thus the compression of the resilient material serves to insure a tight and waterproof ignition assembly. i

The embodiment utilizing resilient material is shown in Fig. 12 wherein/the plug 34 is securely held by the crimps 36 and 31 in the Shell 35, thus forming a watertight connection. In accordance with this embodiment, it is desirable,

to utilize materials of a vulcanizable resilient nature such as crude rubber, rubber substitutes, etc.

The method ofA this invention is equally applicable to the manufacture of other ignition assemblies such as the matchhead type. l

The foregoing method of manufacture, as well as the electric blasting initiator resulting therefrom, offers many advantages over the art. By molding the plug in a separate operation, it has been possible to eliminate the disadvantages inherent in the old procedure of molding the plug around the leg wires. Thus, in accordance with this invention, it is not necessary to handle long lengths of leg wires and to hold the ends thereof in fixed positions in the mold during the molding operation. Further, there is no danger of damaging the insulation on the leg wires nor of causing the intermingling of the insulation material with the plug material.

The utilization of pins, in the manner set forth, results in a procedure which is faster, less complicated and easier to mechanize than heretofore known. It is, therefore, possible to eiect greater economy and production when following the teachings of this invention.

A further advantage resides in the elimination of the hazardous operation of pouring a. molten sealing compound into a shell loaded with explosive. As a result, less handling and manipulating of a sensitive explosive are required.

The electric initiator manufactured in accordance with this invention has greater strength and water-resistant properties, is shorter and less expensive than the ordinary type of device used for this purpose.

This application is a division of my application 4for United States Letters Patent Serial No.

670,795, filed May 18, 1946.

What I claim and desire to protect by Letters Patent is:

1. In the method of producing an electric blast- The plug isV ing initiator the improvement comprising forming a plug of dielectric material having a pair of movg able spaced pins therein and protruding from at least one end of said plug, securing the bare ends of a pair of leg wires tothe adjacent protruding ends of the pins, moving the Pins relative to the plug to embed the bare portions of the wires in the plug. and securing a bridgev wire to the pins adjacent the end opposite the-leg wires. 2. In the method of producing an electric blasting initiator theimprovement comprising forming a plug of dielectric material having a pair of movable spaced pins therein and protruding from at least one end of said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed thebare portions of the wires in theplug, earing the pins adjacent the plug to prevent subsequent pulling out, and securing a bridge wire to the pins adjacent the end opposite 'the leg wires.

3. In' the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a pair of movable spaced pins therein and protruding from at least one end of said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug, earing the pins adjacent the plug to prevent subsequent pulling out, cutting oiI the ends of the pin at a predetermined distance from the plug, and securing a bridge wire tothe pins adjacent the end opposite the leg wires.

4. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material about a pair of movable spaced pins in such manner that the ends of the pins protrude from at least one end of Said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires inthe plug, and securing a bridge wire to the pins adjacent the end opposite the leg wires.

5. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material about a pair of movable spaced pins in such manner that the ends of the pins protrude from at least one end of said plug. securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug. earing the pins adjacent the plug to prevent subsequent pulling out, and securing a bridge wire to the pins adjacent the end opposite the leg wires.

6. In the method of producing an electric blasting initiator the improvement comprising forming avplug of dielectric material about a pair of movable spaced pins in such manner that the ends of the pins protrude from at least one end of said plug, securing the bare ends of a pair of leg wires' to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug, earing the pins adjacent the plug to prevent subsequent pulling out, cutting off the ends of the pin at a, predetermined distance from the plug, and securing a bridge wire to the pins adjacent the end opposite the leg wires.

7. The method of producing an electric blasting initiator comprising forming a plug of dielectric material having a pair of movable spaced pins therein and protruding from at least one end of said plug, securing the bare ends of a pair asis-,vso

of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug. securing a bridge wire to the pins adjacent the end opposite the leg wires, and inserting the plug assembly in the open end of a blasting initiator in watertight relation therewith.

8. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material about a pair of movable spaced pins in such manner that the ends of the pins protrude from at least one end oi said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins' relative to the plug to embed the bare portions of the wires in the plug,

Y securing 'a bridge wire to the' pins adjacent the end opposite the leg wires. and inserting the plug assembly in the open end of a'blasting initiator in watertight relation therewith.

9. The method of producing an electric blast-v ing initiator comprising forming a plug of dielectric material having a pair of movable spaced pins therein and protruding from at least one end of said plug. securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins. moving the pins relative to the plug to embed the bare portions of the wires in the plug, securing a bridge wire to the pins adjacent the end opposite the leg wires, `forming a blasting l Il cartridge the inside dimensions of which are l slightly less than the outside dimensions of the plus. and forcing the plus assembly into the car- 10. The method of producing an electric blasting initiator comprising forming a plug of dielectric material containing a minor amount of wax, said plug having a pair of movable spaced pins therein Aand protruding from at least one end of said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pim relative to the plug to embed the bare portions of the wires in the plus, securing a bridge wire to the pins adjacent the end opposite the leg wires. forming'a blasting cartridge, the inside dimensions of which are slightly less than the outside dimensions -of the plug. and forcing the plug assembly into the cartridge, thereby expanding the outer walls of the cart-gidge and forming aswatertight Joint therewi il. In the method of producing an electric blasting initiator. the improvement comprising forming a plug having a pair of movable spaced pins therein 'and protruding from at least one end of the plug, securing the bare ends of a pair oi' legvwires to the adjacent protruding ends of the pins. moving the pins relative to the plug to embed the bare portions of the wires in the plug,

and providing a resistance initiating means for the pins adjacent the end opposite the leg wires.

EDWARD K. ISEFREN.

No references cited.

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