US2863392A - Delay electric initiators - Google Patents

Description

De 9, 1958 R. Ajw. HILL ETAL 2,863,392

DELAY ELECTRIC INITIAToRs Filed July 18, 195s 2,863,392 Patented Dec. 9, 1958 DELAY ELECTRIC INITIAToRs Royston Arthur Walter Hill and Robert Walter Moody, West Kilhride, Scotland, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Application July 18, 1956, Serial No. 598,584

Claims priority, application Great Britain August 15, 1955 7 Claims. (Cl. 102-28) It has now been found that by using for the delay elep ment a metal tube having its lower end closed and containing a small quantity of a primary explosive composition Ibetween the closed end of the metal tube and the lower end of the column of delay composition it is possible to provide delay detonators which are non-incendiary and which have a high degree of regularity over wide ranges of delay times as for instance delay periods ranging from 20 milliseconds to 5 seconds.

According to the present invention a ventless delay electric deto-nator lcomprising a casing of copper, zinc, copper alloy or zinc alloy containing therein a base charge of a secondary explosive composition and a superimposed charge of a primary explosive composition and having a delay element consisting of a metal tube containing therein a delay fuse composition and interposed between the primary explosive composition and an electric fusehead is characterised in that the lower end of the metal tube is closed and contains a small charge of a primary explosive composition between the closed end thereof and the lower end of the column of delay fuse composition and in that said delay element is so secured in the casing that it is retained on the firing of the detonator.

Said metal tube of the delay element may be of copper alloy or of mild steel but not of aluminium and it must not be deformed to any substantial degree during the loading of the delay composition therein and must not disintegrate on the tiring of the detonator.

The delay element is retained in the casing on explosion of the detonator by for example crimping the casing to the metal tube of the delay element or preferably by having an intervening metal tube of for instance copper, copper alloy, mild steel, zinc or zinc alloy between the delay element and the casing and crimped to the casing. This intervening metal tube is preferably provided with a small aperture in its lbase of smaller diameter than the inner diameter of the metal tube of the delay element. Furthermore the metal tube of the delay element should preferably t tightly in this intervening metal tube.

The diameter, nature and amount of the delay fuse composition in the metal tube of the delay element can be those normally characteristic for delay elements in delay electric detonators. For instance the diameter of the delay fuse composition in the metal tube of the delay element may be 3.3 mm., the length of the column of the delay composition may vary for example between 3 and 30 mm., and the delay fuse composition may be for instance a substantially gasless mixture of oxidising agents and reducing agents for example one consisting of lead dioxide and silicon or potassium permanganate and antimony.

AThe del-ay element should preferably be in contact with the upper surface of the primary explosive composition in the casing so that the shock wave for-med on the detonation of the primary explosive composition in the metal tube of the delay element is transmitted through the bottom of this metal tube and readily initiates the explosion of the primary explosive composition in the casing. As the metal tube of the delay element does not disintegrate but remains intact on the firing of the detonator no hot particles of slag from the delay composition or from the fusehead are ejected on the firing of the detonator and so the danger of ignition of inllammable methane/'air mixtures is removed.

On examination of the delay detonators according to the invention after their ring it is found that although the base of the casing is blown away the metal tube of the delay element remains in position within the casing and that the slag for-med is retained within the casing. Furthermore it has also been experimentally conrmed that hot (luminescent) 4particles are not ejected from the detonators of the inventiony 'when they are red by comparing photographs of the streams of the particles issuing from these detonators when they are tired with those of the streams of the particles issuing from instantaneous copper detona'tors and normal short delay copper detonators when these are fired.

The invention is illustrated by way of example with reference to the diagrammatic drawings accompanying the specification in which 1 is a copper tube, 2 is a base charge, 3 is a superimposed primary charge, 4 is a copper tube which contacts the charge 3 and is provided with a hole 5, 6 is a-mild steel tube having its lower end closed and containing an initiating charge 7 on top of which is a column 8 of delay fuse composition, 9 is an electric fusehead and 10 is a neoprene plug to which the tubes 1 and 4 are crimped and through which pass the leading wires 11 for the electric fusehead 9.

The invention is further illustrated by the following examples.

Example 1 -For a delay detonator of mean delay time of 266 milliseconds copper tube 1 is of an external diameter 7.14 mm. and a length of 65 mm., base charge 2 is 0.25 gram tetryl, primary explosive charge 3 is 0.35 gram of an aluminium/lead azide/lead styphnate composition, copper tube 4 is of an external diameter 6.52 mm. and a length 52 mm., hole 5 is of a diameter 1.90 mm., mild steel tube 6 is of an external diameter 6.02 mm. and internal diameter 3.30 mm., a length 21.5 mm. and a base thickness 0.76 mm., the initiating charge 7 consists of 0.03 gram lead azide and the delay fuse composition 8 consists of lead dioxide/silicon (S0/50) pressed at 18 tons per square inch.

In order to test for instance 25 of these detonators for gas ignition each detonator is suspended in a 9% (by volume) methane/methane air mixture and is tired by a single shot exploder and it is found that not a single detonator ignites the methane air mixture. Each of for instance 30 of these detonators is also tired to determine scatter and it is found that the scatter is 3l milliseconds.

Example 2 Fora delay detonator of mean delay time of 2.26 seconds the dimensions and compositions are the same asin Example. l .except that metal `tube 6' is .of a. length 13.0 mm. and the delay fuse composition 8 consists of potassium permanganate/antimony (36/ 36).

. In order to test for instance, .l'Onof these detonators for Example 3 For a delay detonator of mean delay time of 27 milliseconds the dimensions and compositions are the same as in Example l except that ythe metal tube 6 is of a length mm.

In order to test for instance 25 of these detonators for gas ignition each detonator is suspended in a 9% (by Volume) methane/methane air mixture and is fired by a single shot exploder and it is found. that not a single detonator ignites the methane air mixture. Each of for instance 25 of these detonators is also tired to determine scatter and it is found that theV scatter is 8 milliseconds.

What We claim is:

l. A ventless delay electric detonator comprising 'a metallic casing containing therein a fusehead, a base charge of a secondary explosive composition and a superimposed vcharge of a primary explosive composition and having a delay element including a metal tube containing therein a delay fuse composition, said delay element be- Y ing interposed between said primary explosive composition and said fusehead, said delay fuse composition beingv of the gasless type and said 'metaltube having its lower end nonrupturably sealed against the reaction of its contents and secured so as to be retained in the detonator casing on firing of the detonator, and a small charge of primary explosive composition being disposed within said metal tube between the gasless delay composition and the .closed end of the tube.

2. A ventless delay electric detonator as claimed in claim 1 wherein said metal tube is formed of a material selected from the group consisting of a copper alloy and mild steel.

V3. A ventless electric detonator according to claim l wherein said casing is crimped to said metal tube.

4. A ventless electric delay detonator comprising a metallic casing, a base charge of a secondary explosive, a superimposed charge of a primary explosive composition and a fusehead in said casing, a delay element in said casing comprising a metal tube containing therein a delay fuse composition and interposed between said primary explosive composition and said fusehead, said delay composition being of the gasless type and said metal tube having its lower end nonrupturably sealed against the reaction of its contained constituents, a small quantity of a primary explosive composition disposed `Within said tube between lthe delay composition yand the closed end of said tube and an intervening second metal tube between said casing and said delay element tube, said second tube being assembled to retain the delay element tube Within the detonator-casing upon firing of the detonator.

A 5. A ventless electric detonator as claimed in claim 4 wherein said' second metal tube has a basal aperture of smaller diameter than that of the interior of said delay element metal tube.

6. A ventless electric detonator as claimed in claim 4 wherein said gasless delay fuse composition is a substantially gasless mixture of lead dioxide and silicon.

7. A ventless electric detonator as claimed in claim 4 wherein said gasless delay fuse composition is a substantially gasless mixture of potassium permanganate and antimony.

References Cited in the file of this patent UNITED STATES PATENTS Australia May 2l,

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