GB843071A - Improvements in or relating to electric initiators - Google Patents

Abstract

843,071. Electric blasting detonators. DU PONT DE NEMOURS & CO., E. I. Aug. 5, 1958 (Sept. 9, 1957], No. 25116/58. Class 9(1) An electric detonator comprises an open-ended tube 1 surrounding a thickwalled rigid cylinder 2 having an axial bore filled with between 0.025 and 0.65 grains of lead azide with a distribution density of 2.5 to 60 grains per foot, the tube being closed at one end by the electric ignition assembly which on passage of a current fires the lead azide. The lead azide may be mixed with PETN or nitromannite. The cylinder is made of rigid material which does not react with the lead azide e.g. lead, aluminium or steel or polymerised materials, and preferably, the ratio of the outer to the inner diameter is two or more. The tube 1 may be made of metal or plastics. A thin metal capsule may be fitted over the outer end of the cylinder 2. The ignition assembly may comprise a bridgewire 4 connecting leads 5 extending through a resilient plug 6, the wire 4 being embedded in an ignition composition either in the form of a bead 8 or a loose charge such as a boron and red lead mixture. Alternatively a bridgewire may be used, which volatilizes on the passage of a large current with the ejection of particles of hot metal and so ignites the lead azide. Ignition may be also by a spark produced between the ends of the leads embedded in the ignition composition. The detonator is crimped over the free end of a detonating fuze cord 9. The ignition composition may be a mixture of silicon and red lead, manganese and bismuth trioxide, lead sulphocyanate with potassium chlorate and calcium silicide, bismuth with selenium and potassium chlorate, or diazodinitrophenol and potassium chlorate. A single compound such as lead styphnate, tetrazene or a loose charge of lead azide may also be used as the ignition charge. Specification 564,211 is referred to.