GB752724A - Improvements in or relating to electrical pellet primers - Google Patents

Abstract

752,724. Electric igniters. MENKE, J. F.; and DOERPINGAUS, E. H. July 19, 1954 [July 17, 1953], No. 20980/54. Classes 9(1) and 9(2) An electric igniter for blasting cartridges, projectile fuzes, propellants and flash powders comprises leg wires 2, 3 passed through a glass bead 1 coated with an electrically conductive metal such as platinum. The thickness of the coating may be sufficient to produce a resistance of 40 to 100 ohms between the two wires. Over this coating is a layer of a priming composition, such as cuprous carbide, covered by a layer of thermally insulating material, such as nitrocellulose, separating the primer from a surrounding detonating charge 5, which may be lead azide. The charge 5 is in a casing 6 closed at one end by a destructible membrane 7 and at the other end by a plate 8, the closures being secured by beadings 9, 10. Extending through the plate 8 is a contact 11 mounted in an insulating sleeve 12 and housing the outer end of leg wire 2. The second leg wire 3 extends along a groove in the periphery of the plate 8. In a modification, Fig. 2, the wires 2, 3 project at both ends from the bead 1, the shorter wire 3 being engaged in grooves in a contact member 13 surrounded by an insulator 14, which fits within a metal sleeve 15. Grooves in the sleeve 15 receive the ends of the leg wire 2 and are clamped by a, cap 16 which holds the charge 5, part of which extends into the contact member 13. A flash passage 19 in the cap 16 communicates with a chamber 20 of the ignition device. The wires 2, 3 may be a nickel-chrome alloy. To produce the igniters, two parallel wires are passed through a, machine in which glass beads are fused at regular intervals to the wires and the resultant chain is passed through a metal salt solution. The coating is heated to reduce the salt to metal and the process repeated until the required thickness of metal is deposited on the beads. The bead chain is then calcined to bond the metal to the glass. The layer of priming composition may be deposited on the bead from a solution or applied by pressing. On completion of the coatings the wires are cut between the beads. For the detonator of Fig. 1 the wires may be inserted in the plate 8 prior to cutting. When making the fuze shown in Fig. 2, the wire 3 is cut intermediate the beads and the beads are connected to the contacts 13, 15 prior to cutting the wire 2. The beads may be made of ceramic materials. Specification 652,802 is referred to.