US2619035A - Production of ventless delay initiators for explosive or other charges capable of exothermic reaction - Google Patents

Description

952 o. LEWIS ET AL 2,619,035

PRODUCTION OF VENTLESS DELAY INITIATORS FOR EXPLOSIVE oR OTHER CHARGES CAPABLE OF EXOTHERMIC REACTION Filed Nov. 1, 194a lnvenlorzs- [a'wal Owerzlewz's id 13 RoberlDavid Jo/z Owens A Home Patented Nov. 25 1952 Units RRODUCTION OF VENTLESS DELAY INI- TIATORS FOR EXPLOSIVE OR OTHER CHARGES CAPABLE OF EXOTHERIWIC REACTION tion of Great Britain Application November 1, 1948, Serial No. 57,776 In Great Britain December 31, 1947 3 Claims.

The present invention relates to improvements in the production of ventless delay electric initiators, that is to say devices for effecting the excitation of the required reaction in explosive or other charges capable of exothermic reaction, these initiators being of the kind wherein an electrically actuated igniting charge, an initiating charge and an interposed delay fuse element are enclosed in a ventless container and the said igniting charge and delay fuse element produce an insufficient amount of gases or vapours to break the closure of the container before the ignition of the initiating charge has been effected. Amongst the advantages of this kind of delay electric initiator are the ease with which moisture can be excluded from its interior, and the fact that no incandescent products or flames are ejected while the igniting charge and the delay fuse are being consumed, which latter advantage is often of special importance in the case of the kind of delay electric initiators required for detonating explosives, as in blasting operations. In this kind of delay electric initiator, namely a delay electric detonator, the initiating charge comprises a detonating explosive, and ventless delay electric detonators have found extensive application in blasting operations where it is required that explosive charges connected up in a single circuit should detonate successively with predetermined intervals between the detonations.

It is an object of the present invention to provide new or improved ventless delay electric initiators, for example ventless delay electric detonators, whose production can be more expeditiously, economically or conveniently effected than that of the known ventless electric initiators.

Hitherto the delay fuse elements employed in commercial delay electric initiators have usually comprised each a length of rigid metal tubing into which the powdered delay composition that yields little or no gas or vapour as it is consumed is introduced in increments, each of which increments is highly compressed into said length of tubing before the next increment is introduced. For a given composition the number of pressings required depends mainly on the length of the column of the compressed composition required to provide the required delay interval. This incremental loading has hitherto been regarded as essential in order to give the composition the necessary mechanical strength and to ensure that the packing should be to a uniform density all along the length of the column, so that a rigid tube of a given length loaded with the same composition will always give the same delay period. The rigid metal tube so charged with the gasless delay composition is pushed into the tubular container of the initiator, in which it must form a tight fit so that no annular space is left by which flame can travel directly from the igniting charge to the initiating charge, and so that it will be secured from sliding motion in the free space.

It would be desirable to increase the rate at which ventless delay detonators can be produced, and especially desirable to increase the rate of production of delay fuse elements, hitherto requiring to be loaded in a multiplicity of increments.

According to the present invention a ventless delay electric initiator is characterised in that the delay fuse element thereof consists of a flexible envelope surrounding an unbroken continuously extruded core of a thermoplastic composition of low gas evolution characteristics comprising inorganic reducing agent and oxidising agent powders adapted on ignition to react exothermically with the formation of non-volatile products accompanied by at most insignificant amounts of volatile products, said reducing agent being present in at least the stoichiometric proportion, embedded in a continuum of an organic thermoplastic.

In accordance with a preferred embodiment of the present invention a ventless electric initiator has a delay fuse element cut off from a length of a fuse having a flexible envelope surrounding an unbroken continuously extruded core of a thermoplastic composition of low gas evolution characteristics comprising inorganic reducing agent and oxidising agent powders adapted on ignition to react cxothermically with the formation of non-volatile products accompanied by at most insignificant amounts of volatile products, said reducing agent being present in at least the stoichiometric proportion, embedded in a continuum of an organic thermoplastic.

The core may if desired be extruded around a filament, the nature of which will have an effect on the linear burning speed of the delay fuse.

In accordance with a further preferred embodiment of the invention the delay fuse element is secured in. position by pressing a perforated inverted metal cup over the end thereof remote from the initiating composition, instead of relying on a friction fit between the textile envelope and the wall of the tubular container. The use of such a cup also prevents the textile envelope from being ignited by the electric fusehead or the like and is especially convenient when an additional igniting composition for the thermoplastic core composition is present. The organic thermoplastic may be one of low infiammability, for instance a thermoplastic based on a polymerised vinyl, acrylic or methacrylic derivative or a cellulose organic ester or cellulose ether, and the oxidising and reducing agents may advantageously comprise red lead and silicon.

The composition of the extruded core is preferably so adjusted that no matter how short the delay time required the length of the fuse element cut off will exceed its diameter.

In inserting the delay fuse elements used according to the present invention into the tubular containers, the soft and somewhat compressible nature of the textile envelope renders the attainment of the necessary tight fit easy without the application of loading pressures so high that the core shows any tendency to crumble in the course of the operation. An expansion space must be left between the end of the delay fuse element and the closure. If desired or necessary a small charge of supplementary preferably gasless igniting composition may be interposed between the end of the delay fuse element and the characteristic charge of the initiator. It is also sometimes desirable to press a small charge of a gasless igniting composition directly on top of the delay fuse element in order to ensure its ignition from the electrically ignitable charge, which will usually be spaced from it. The electrically ignitable charge may take the form o an electric fusehead.

Since the delay period is controlled by the length of delay fuse element cut off from the greater length, delay electric initiators of relatively long delay characteristics can be produced as quickly as those of relatively short delay characteristics according to the invention, and the cutting of a length of plastic core fuse is a more expeditious operation than the pressing of even a single charge into a rigid metal tube.

The invention is further illustrated by the diagrammatic drawing accompanying the specification, which represents a vertical axial section of one form of delay electric initiator, more particularly a delay electric detonator, in accordance with the invention.

In the drawing 1 is an aluminum detonator tube, 2 is a detonating explosive charge of tetryl compresssed into the end of the tube and 3 is a more sensitive detonating explosive charge compressed on top of the charge 2 and consisting essentially of a mixture of lead azide, and lead styphnate, 5 is the envelope of waterproof coated textiles, and 0 is the thermoplastic core composition of a delay fuse element cut off from a length of delay fuse having a textile envelope surrounding an unbroken continuously extruded core of for example a 75:25 mixture of red lead, silicon and a plastic consisting of methyl methacrylate polymer and dibutyl phthalate in equal proportions, the proportion of the active ingredients to the plastic being 90:10 all these proportions being by weight. The diameter of the core is approximately 2 millimetres. I2 is a 36 S. W. G. central copper wire filament around which the thermoplastic core composition 6 has been extruded. i is a layer of a gasless igniting composition consisting for instance of antimony and potassium permanganate in the ratio 30:70 by weight. 1 is a layer of the same composition as composition 4, and 8 is a perforated inverted metal cup pressed over the composition 1 and over the top end of the delay fuse envelope 5 so as to secure the delay fuse element longitudinally in the tube and effectually seal off the space above this cup from the composition 4. 9 is an electric fusehead, ll and H are insulated electric leading wires and I9 is an axially perforated sealing plug of rubber like material crimped between the metal tube 1 and the wires II and H as shown at [3, whereby there is attained a seal capable of withstanding an internal pressure greater than the maximum pressure that can be produced up to and including the time required for combustion of the intermediate charge 4. The space it between the end of the plug l0 and the inverted cup 8 and hence the length of the tube I is accordingly sufficient to ensure that the hot pressure developed in the initiator by the successive consumption of the compositions of the electric fusehead 9, the igniting charge I, the core composition 5 of the delay fuse element together with any gases that may arise from charring of its envelope 5, and the igniting charge 4 will not unseal it. The length of the aforesaid delay fuse element required is about 0.7 centimetre per second of delay period.

We claim:

1. A delay electric detonator comprising an electrically actuated igniting charge, an initiating charge, and an interposed delay fuse element consisting of a length cut off from a fuse comprising a flexible envelope surrounding a charge based on inorganic reducing agent and oxidizing agent powders enclosed in a detonator tube, said flexible envelope surrounding an unbroken continuously extruded core of a thermoplastic composition of low gas evolution characteristics comprising inorganic reducing agent and oxidizing agent powders embedded in a continuum of an organic thermoplastic and adapted on ignition to react exothermically with the formation of non-volatile products accompanied by at most insignificant amounts of volatile products, said reducing agent being in at least the stoichiometric proportion, and said thermoplastic being of low inflammability and selected from the group consisting of vinyl, acrylic, methacrylic, cellulose organic esters and cellulose ether polymers, so as to form a ventless delay initiator.

2. A ventless delay electric initiator as set forth in claim 1 wherein the said core of thermoplastic composition of low gas evolution characteristics includes a central filament.

3. A ventless delay electric initiator as set forth in claim 1 wherein the oxidizing and reducing agent powders comprise red lead and silicon.

IDVVAL O. LEWIS. ROBERT D. J. OWENS.

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

UNITED STATES PATENTS Number Name Date 1,825,224 Ellsworth Sept. 29, 1931 2,139,581 Hanley Dec. 6, 1938 2,410,801 Audrieth NOV. 12, 1946 FOREIGN PATENTS Number Country Date 580,409 Great Britain Sept. 6, 1946

Claims (1)

1. A DELAY ELECTRIC DETONATOR COMPRISING AN ELECTRICALLY ACTUATED IGNITING CHARGE, AN INITIATING CHARGE, AND AN INTERPOSED DELAY FUSE ELEMENT CONSISTING OF A LENGTH CUT OFF FROM A FUSE COMPRISING A FLEXIBLE ENVELOPE SURROUNDING A CHARGE BASED ON INORGANIC REDUCING AGENT AND OXIDIZING AGENT POWDERS ENCLOSED IN A DETONATOR TUBE, SAID FLEXIBLE ENVELOPE SURROUNDING AN UNBROKEN CONTINUOUSLY EXTRUDED CORE OF A THERMOPLASTIC COMPOSITION OF LOW GAS EVOLUTION CHARACTERISTICS COMPRISING INORGANIC REDUCING AGENT AND OXIDIZING AGENT POWDERS EMBEDDED IN A CONTINUUM OF AN ORGANIC THERMOPLASTIC AND ADAPTED ON IGNITION TO REACT

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