GB902643A - Improvements in or relating to electric detonators - Google Patents

Abstract

902,643. Electric detonator and matchhead compositions therefor. IMPERIAL CHEMICAL INDUSTRIES Ltd. Sept. 23, 1960 [Oct. 2, 1959], No. 33450/59. Classes 9 (1) and 9 (2). Relates to an electric detonator having no primary initiating explosive and containing an electric fuzehead of high or low tension characteristics with a gas-producing matchhead composition pellet 5 in which at least one of the high-tension polepieces 10 or the resistance bridgewire 14 is embedded. According to the invention, the pellet 5 is housed in a stout metal walled tube 6 adjacent the end of the tube which is nearer the mouth of the detonator casing 1, and confined by a polystyrene or like plug 7 so that there is no outlet for the combustion gases permitting them to bear on the neoprene seal 12. A column 3 of composition preponderantly pentaerythritol tetranitrate is uniformly and incrementally compressed against the pellet 5 at a pressure of not less than 1500 kg. cm<SP>-2</SP> while a base charge 2 of a secondary initiating explosive is compressed into the detonator casing 1 at a pressure of not more than 300 sq. cm<SP>-2</SP> such that a space remains between the P.E.T.N. and the base charge. The matchhead composition for high tension use as in Fig. 3 is rendered conducting by the inclusion of graphite, e.g. 10% graphite and 90% potassium chlorate, while for low tension use, the pellet, in Fig. 4, is non-conducting and is of compressed P.E.T.N. powder, or of 87% potassium chlorate and 13% charcoal: the bridgewire in the latter stage may be a Ni/Cr/Fe alloy.