GB757775A - Improvements in detonating devices - Google Patents

Abstract

757.775. Blasting devices. DU PONT DE NEMOURS & CO., E. I. Sept. 10 1954, No. 26235/54. Classes 9(1) and 68(1) A delay device for connecting lengths of detonating fuze 1, 1<SP>1</SP> comprises a metal tube 3 enclosing a thick-walled lead tube 5 at each end of which are exothermic charges 6, 6<SP>1</SP> held in place by blind metal capsules 7, 7' in contact with heat-sensitive charges 8 8' which adjoin detonating charges 9,' 9<SP>1</SP>. Metal capsules 10, 10<SP>1</SP> confine the charges 8, 9 and 8<SP>1</SP>, 9<SP>1</SP> respectively. The inner capsules 7, 7' have bases four times the thickness of their walls at the open ends and are crimped to the lead tube. On detonation of the charge 9 by fuze 1, capsule 7 is indented through the charge 8 and charges 6, 6' are thereby ignited. The heat evolved by the charges 6, 6<SP>1</SP> ignites after a delay the heat-sensitive charge 8' to promote detonation of charge 9<SP>1</SP> which initiates the the fuze 1<SP>1</SP>. The action is reversible so that detonation of fuze 1 may be brought about by fuze 1'. In a modification, heat-sensitive charges 8, 8' are held at each end of the empty lead tube by conical-ended capsules extending into detonating charges 9, 9<SP>1</SP>. The charges 8, 8' may be a 30/35, 35 mixture of magnesium, barium peroxide and selenium.. The detonating fuze may be cordeau, primacord or cyclotrimethylenetrinitramine and the detonating charge in the delay device may be lead azide, mercury fulminate or diazodinitrophenol. The exothermic charge may be a mixture of magnesium, barium peroxide and selenium or bismuth, selenium and potassium chlorate. For the heat-sensitive charges 8, 8' mixtures of bismuth, selenium and potassium chlorate or aluminium, tetrazene and mannitol hexanitrate or mercury fulminate or diazodinitrophenol may be used. Instead of lead, any rigid non-combustible material may be used for the tube 5, e.g. brass, aluminium or a synthetic plastic such as nylon. In an example according to Fig. 1, the delay connector contained detonating charges of lead azide 4 grains, the heat-sensitive charges were 1.0 grains of 50/25/25 Al/tetrazene/mannitol hexanitrate and the exothermic charges were 1.5 grains of a 30/35/35 Mg/BaO 2 /Se mixture in gilding metal capsules with bases 0.027 in. thick. The lead tube was 1 in. long and of internal diameter 0.073 in. to give a delay of 17 milliseconds. Fig. 3 shows an arrangement of boreholes containing blasting charges, e.g. 60 per cent ammonia gelatine dynamite, connected together by detonating fuze cord, so that on firing an electric blasting cap 23 the firing of all the explosive in the first line of boreholes takes place almost instantaneously. Delay devices 21a, 21b, 21c, according to the invention, connect the cord of the first line to a second line of boreholes, so that the second line is fired after a short delay. Should there by a failure in a length of detonating fuze between two holes, the charge in the second hole may still be initiated since the delays 21 can transmit fire in two directions. Specification 588,613 is referred to.