US3122097A

US3122097A - Non-electric initiating assembly

Info

Publication number: US3122097A
Application number: US144140A
Authority: US
Inventors: Miller Ross Jay
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1961-10-10
Filing date: 1961-10-10
Publication date: 1964-02-25
Anticipated expiration: 1981-02-25

Description

Feb. 25, 1964 R. J. MILLER 3,122,097

NON-ELECTRIC INITiATING ASSEMBLY Filed Oct. 10, 1961 FIG. F|G.2

INVENTOR ROSS JAY MILLER BY g A.

ATTORNEY United States Patent 3,122,097 NON-ELECTRIC INITIATlNG ASSEMBLY Ross Jay Miller, Pitrnan, NJ., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware Filed Get. 10, 1961, Ser. No. 144,149 6 Claims. (Cl. 102-27) tained within a sheath of a ductile metal which is sub-' sequently covered with one or more layers of reinforcing and/or waterproofing material. Due to its ability to propagate a detonation impulse without attendant brisance and because it is free from the hazards associated with electric initiators, in many blasting operations this cord has replaced conventional detonating fuse and electrical initiators.

However the aforedescribed cord, owing to the low loading of explosive contained in the core, does not initiate the explosive compositions conventionally used in blasting. Consequently, auxiliary means are needed to relay the detonation stimulus from the low-energy connecting cord to the explosive charges to be initiated. In cases where it is desirable to provide a delay interval between initiation of the main explosive charges to permit the burden loosened by a proceeding blast to clear, to reduce ground vibration, and to improve fragmentation, a delay initiator actuated by the connecting cords detonation can be used.

In accordance with this invention, there is provided a non-electric initiating assembly comprising a tubular shell integrally closed at one end, said shell housing, in sequence from said closed end, a base charge of detonating explosive, a priming charge of a heat-sensitive detonating explosive, and a charge of an exothermic-burning composition, a tubular capsule positioned within the said shell contiguous to said exothermic burning composition, said capsule having a closure at one end provided with a central aperture therethrough, and a looped section of low-energy connecting cord extending into the said shell, the lower looped portion of said cord being positioned adjacent to said capsule and in igniting relationship to said exothermic burning composition.

In a preferred embodiment of this invention, the looped section of the cord is of U-shaped configuration. In a particularly preferred embodiment of this invention, a perforation, e.g., a pin hole or slit is provided in at least a portion of the countering of the looped section of the cord. In a still further embodiment of this invention, the looped section of cord is positioned in the shell by means fo a plug of a resilient composition which is in snug peripheral engagement with the inner walls of the rigid shell of the auxiliary initiator.

In order to describe the invention in greater detail, reference is made to the accompanying drawings wherein:

FIGURE 1 is a cross-sectional drawing of an initiating assembly in accordance with this invention and FIGURE 2 is a cross-sectional drawing of a modification of this invention adapted to give a delayed initiating action.

In FIGURE 1, 1 represents a tubular shell having one integrally closed end, 2 represents the connecting cord consisting of explosive core 3, metal sheath 4, and countering 5. The looped section 6 of the cord 2 is held within a plug 7 which closes the open end of shell 1. Within shell 1 are, in sequence, a base charge 8 of a detonating 3,122,097 Patented Feb. 25, 1964 explosive, a priming charge 9 of a heat-sensitive detonating explosive, an exothermic-burning composition 10, and a spacing means, i.e., an open-ended capsule 11, having a central aperture 12. An air gap 13 is formed within the space enclosed by capsule 11. Peripheral crimps 14 hold the plug and cord 2 in place.

The assembly depicted in FIGURE 2 is identical to that of FIGURE 1 except that a delay carrier 15 containing a delay composition 16 is interposed between the primer 9 and the exothermic burning composition 10.

In operation of the initiator, the initiation impulse propagated by the detonation of the explosive cord is transmitted from the explosive core through the lead sheathing in the looped section of the cord, probably with the formation of hot, minute missiles of the ductile metal, jumps the air gap 13 enclosed by the capsule 11, passes through aperture 12 and ignites the exothermic burning delay composition 10. This composition burns at high temperature, and when the hot front reaches the priming charge 9, the latter is ignited. The priming charge, in turn, initiates the base charge 8. The initiator of the design of FIGURE 1 can be designed to provide a precise delay of from 1 to 1000 milliseconds, the length of the delay period depending upon the depth of the exothermic burning composition, since the burning time of the exo thermic burning charge is proportional to the depth of this charge. A longer delay, e.g., l-ZO seconds, is provided by the assembly of FIGURE 2 wherein the exothermic burning composition 10 ignites delay composition 16 in the delay carrier 15. This delay composition in turn ignites the priming charge 9.

While it is not desired for this invention to be limited by theory, it is believed that the improved initiation characteristics provided by the looped section of low-energy cord is due to increased confinement of the explosive core of the lowenergy connecting cord so that a doublebarrelled initiation effect is achieved. That is, a portion of the detonation impulse is propelled through the looped section directly in the form of a front of hot lead particles, reaction products, and flame, while a remaining portion is transmitted through the folded back section of cord with the result that there is a propulsion of detonation products and flame through the looped section.

When low loadings of explosive are used in the core, i.e., less than about 1.0 grains per foot, or the countering on the cord is relatively thick, it is preferred to perforate the looped section so that the major portion of the detonation impulse will be transmitted from the looped section of cord to the exothermic burning composition and not expended in burning through the countering. The perforation which may be provided in the looped section of the cord may be a pinhole or slit, or an entire section of the countering may be removed from the looped section of the cord either by cutting as with a knife or by otherwise stripping away a section of the countering. The sheathing of ductile metal should not be cut. Rupture of this sheathing may result in loss of the explosive core and subsequent cut-off of the detonation impulse.

The looped section 6 of the cord 2 may be formed simply by folding the cut end of the cord 2, to be inserted in initiator shell 1, back upon the length of cord 2 at an angle of about to At angles less than about 95 the double barrelled initiation effect is not achieved and housing problems are encountered. At angles greater than about 180, the lead sheathing may be ruptured with subsequent loss of the explosive core. For low-energy connecting cord having an explosive loading of 0.5 to 2.0 grains per foot, it has been determined that the length of the folded back segment of cord should be at least about /4 inch, i.e., the distance from the end of the cord to the vertex of the angle should be about A inch. This folded-back segment insures that sulficient backward propulsion of detonation products will occur to initiate even very insensitive exothermic compositions over an air gap up to one inch. The looped section of cord also may be provided simply by tying a knot in the end of the cord to be inserted into the initiator.

The air gap or distance between the lower portion of the looped section of cord and the exothermic burning composition may be regulated, e.g., to focus the initiation impulse, by the provision of an appropriate spacing means which also acts to hold the exothermic burning composition in position. This spacing means preferably is a capsule whose depth may be varied and which is provided with a central aperture. The low-energy connecting cord may be inserted in the device until it reaches the bottom of the capsule or may be spaced from the open end of the capsule, provided that the distance between the lowermost portion of the looped cord to the delay composition does not exceed one inch. A separation greater than one inch results in unreliable functioning of the device. Within this range, from contact up to one inch, however, exceptionally reliable performance was obtained in testing the initiators. Obviously, the allowable variance is an asset in the use of initiators in the field since this allows reliable initiation even though the cord should be inadvertently pulled or moved during the blasting operation.

It is preferred that the open-ended spacing capsule be positioned with the open-end directed away from the loaded charges as the rounded corners of the capsule thus inserted act as a retaining medium for the adjacent exothermic-burning composition. However, the capsule may be positioned so that the open-end is directed toward the charges. The dimensions and shape of the aperture in the capsule are not critical. The aperture is present in the capsule in order to facilitate transmission of the initiation impulse from the detonation of the explosive core of the connecting cord to the delay composition. As long as there is an opening in the capsule, this condition will be satisfied.

In order to illustrate specific embodiments of this invention, reference is made to the following examples. These examples are to be understood to be illustrative only and not limiting the invention in any way.

Example 1 Twenty initiators were prepared resembling that of FIGURE 1. In each case, the aluminum shell 1 1 inch in length, 0.278 inch in outside diameter had a 0.010-inch wall thickness. As a base charge, 7.2 grains of PETN was charged to each shell and compacted at 200 pounds by a pointed pin. Above this charge, 3.0 grains of lead azide, as the primer, was loaded and compacted at 200 pounds by a fiat pin. The exothermic-burning composition, 5.0 grains of a 1/99 mixture of boron/red lead, grained with neoprene, was charged to each shell and compacted at 200 pounds by a dimpled pin. An openended aluminum capsule, 0.187 inch long and having a central aperture 0.080 inch in diameter was inserted on top of the exothermic burning composition with the open end directed away from the loaded charges. The end of a length of low-energy connecting cord having 1 grain of lead azide per foot of length contained in a split plug of polyethylene mating with the shell, was turned back into the split to form a U-shaped loop wherein the length turned back section was /8 inch. A slit was made in the countering of this looped section of the cord. The plug containing the cord was inserted into the assembled initiator until there was an air gap of 0.67 inch between the looped cord and the exothermic burning composition. When fired, these units were initiated at low velocity, i.e., the low energy cord was actuated by a length of Primacord. All functioned properly.

When an identical initiator was tested with a square-cut end of the low energy detonating cord, ignition of the exothermic burning composition was not effected.

4 Example 2 Delay initiators were assembled as in Example 1 except that the air gap between the base of the looped section of the cord and the exothermic burning composition, the explosive loading of the core, and the length of the turned back section were varied.

A long-period delay initiator was assembled in an aluminumsheil having essentially the same dimensions as the shell discussed in Example 1 except that a longer length was required in order to accommodate the charges. PETN and lead azide, as the base and priming charge, re spectively, were loaded and compacted as in Exampie l. A delay carrier having a length of 1.063 inch and a shellwall thickness of 0.063 inch and containing a core of a 83/17 barium oxide/ selenium mixture, as a slow-burning delay composition, was placed adjacent to the primer. On top of the carrier 1 grain of the exothermic burning mixture of Example 1 was loaded and pressed at 200 pounds by a fiat pin. The open-ended aluminum capsule was inserted as previously exemplified.

The looped end low-energy connecting cord containing 1 grain of lead azide per foot of length (/2 inch turnback) was inserted into the polyethylene plug, and the plug and cord assembly inserted into the shell leaving an air gap of /s inch. Upon being fired, the initiator gave a delay period of 5.4 seconds.

The plug used to position the looped section of the lowenergy connecting cord within the initiator shell may be formed of any material which is resilient, thermally stable, and of sufiicient structural strength to securely hold the cord within the shell under the conditions of use. The dimensions of this plug naturally will depend upon the size of the shell and the physical properties of the material used. Exemplary of suitable materials of construction for the plug are natural and synthetic rubbers and relatively long-chain polymers, e.g., polyethylene, polypropylene, neoprene, polyvinylidene chloride, polytet-rafiuoroethylene, and the like.

The particular compositions used for the various charges are not critical to the present invention, provided that the selected compositions function as desired. Accordingly, for the base charge, any of the usual base changes may be used, e.g., RDX, lead azide, PETN, nitromannite, TNT, or HMX. As the priming charge, heat sensitive detonating compositions such as lead azide, diazodinitrophenol, or mercury fnlminate may be used. Obviously when squib action is desired, the priming composition and the base charge may be identical. For the exothermic burning composition, an exothermic reacting mixture of a metal and an oxidizing agent of the type conventionally used in ventless delay initiators is preferred, e.g., boron-red lead, boron/red lead/dibasic lead phosphite, magnesium/barium/peroxide/selcnium, or silicon/red lead. For long-period delay initiators, the delay composition within the delay carrier may be any of the conventional, gasless delay compositions which burn at a constant rate, such as a mixture comprising barium peroxide and selenium; bismuth, selenium, and potassium chlorate; lead and selenium; or magnesium and barium peroxide. The amount of each charge is varied depending upon the efiect desired. The composition of the rigid shell surrounding the changes or spacing the charges is not critical; however lead or aluminum is preferred for ease in handling and loading.

The base charge and priming charges may be compacted by various shaped pins, e.g., pointed, flat, conical or bell. Any compaction pressure sufiicient to retain the charges in the shell yet insufiicient to cause densitization of the charges is suitable.

The delay period is dependent upon the depth of the delay charge and amount of compaction of the exothermic burning composition. Accordingly, change in these variables will produce change in the delay period. The limits of pressure used to compact this charge are identical to those used for the base and priming charge, i.e., sufiicient to retain the composition in the shell without densitizing the charge. If desired, the exothermic-burning composition used may be grained prior to use for example, with neoprene, gum, shellac, polyethylene glycol, Thiokol, and carbowaxes. The graining facilities loading but is not critical to the functioning of the device.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is accordingly to be understood that within the scope of the appended claims the invention may be practiced otherwise than specifically described.

What is claimed is:

1. A non-electric delay initiator comprising a tubular shell integrally closed at one end, said shell housing, in sequence from said closed end, a base charge of detonating explosive, a priming charge of a heat-sensitive detonating explosive and a charge of exothermic burning composition; a tubular spacer capsule positioned within the shell contiguous to said exothermic burning composition, said capsule having one closed extremity with a central aperture therethrough; and a section of low energy connecting cord extending into the shell, the lower portion of said cord being looped and positioned adjacent to said capsule a distance of not greater than one inch from, and in igniting relationship to, said exothermic burning composition; said initiator being adapted to provide a delay period of from :1 millisecond to 20 seconds.

2, The initiator as claimed in claim 1, wherein the looped section of said low-energy connecting cord is of U-shaped configuration.

3. The initiator as claimed in claim 1, wherein a plug of a resilient material having an axial aperture there 6 through seals the open extremity of said shell, and wherein the looped section of low-energy connecting cord passes through the axial aperture in said plug and is held in initiating relationship to sai exothermic burning composition thereby.

4. The initiator as claimed in claim 1, wherein a perforation is provided in at least a portion of the countering of the lower looped section of the said cord.

5. The initiator as claimed in claim 1, wherein a delay carrier comprising a heavy-Walled tube of a rigid material containing a central core of a delay composition is interposed between said priming charge and the exothermic-burning composition.

6.. A non-electric delay initiator comprising a metal tube integrally closed at one extremity, said tube housing in sequence from said closed extremity, a base charge of detonating explosive, a priming charge of a heat-sensitive detonating explosive and a charge of exothermic burning composition, a length of low energy connecting cord, extending into said tube, said cord comprising a continuous core of a detonating explosive at a loading of from 0.5 to 2 grains per foot encased in a sheath of ductile metal, the extremity of said cord Wtihin the tube being looped in a U-shaped configuration and positioned to provide a distance of greater than Zero to one inch between said exothermic burning composition said loop, and a capsule having a closed extremity with a central aperture therethrough positioned within said tube between said loop and said exothermic burning composition, said capsule being adapted to focus the initiation impulse which is propagated through the sheathing and countering of said cord at essentially the apex of said loop, and to maintain the proper spacing between said loop and the exothermic burning composition.

References tlited in the file of this patent UNITED STATES PATENTS 2,360,698 Lyte Oct. 17, 1944 2,400,103 Cobb May 14, 194-6 2,402,235 Burrows et a1. June 18, 1946 2,558,134 Hall June 2-6, 1951 2,619,035 Lewis et a1. Nov. 25, 1952 3,021,785 Hradel et al Feb. 20, 196 2 FOREIGN PATENTS 15,806 Germany Oct. 22, 1881 815,532 Great Britain June 24, 1959

Claims

1. A NON-ELECTRIC DELAY INITIATOR COMPRISING A TUBULAR SHELL INTEGRALLY CLOSED AT ONE END, SAID SHELL HOUSING, IN SEQUENCE FROM SAID CLOSED END, A BASE CHARGE OF DETONATING EXPLOSIVE, A PRIMING CHARGE OF A HEAT-SENSITIVE DETONATING EXPLOSIVE AND A CHARGE OF EXOTHERMIC BURNING COMPOSITION; A TUBULAR SPACER CAPSULE POSITIONED WITHIN THE SHELL CONTIGUOUS TO SAID EXOTHERMIC BURNING COMPOSITION, SAID CAPSULE HAVING ONE CLOSED EXTREMITY WITH A CENTRAL APERTURE THERETHROUGH; AND A SECTION OF LOW ENERGY CONNECTING CORD EXTENDING INTO THE SHELL, THE LOWER PORTION OF SAID CORD BEING LOOPED AND POSITIONED ADJACENT TO SAID CAPSULE A DISTANCE OF NOT GREATER THAN ONE INCH FROM, AND IN IGNITING RELATIONSHIP TO, SAID EXOTHERMIC BURNING COMPOSITION; SAID INITIATOR BEING ADAPTED TO PROVIDE A DELAY PERIOD FROM 1 MILLISECOND TO 20 SECONDS.