Patent GB-739770-A (GB)
Title: Improvements in or relating to static resistant electric initiator
IPC: F42B3/185
Filed: 1954-05-12
Abstract: 739,770. Blasting detonators. HERCULES POWDER CO. May 12, 1954 [Nov. 9, 1953], No. 13935/54. Class 9(1). A static resistant electric initiator comprises a dielectric shell, a semi-conductive body disposed about and in conductive relationship with bared portions of both the lead wires of said initiator and an ignition composition disposed about the bridge wire interconnecting the lead wires, the arrangement being such that the shell forms a non-conductive layer between the semi-conductive body and ground of less thickness than the distance between either lead wire and ground in the locus of the ignition composition whereby the path from either lead wire to grounded shell has less total resistance through the semi-conductive body outside the locus of the ignition composition than in said locus. The initiator, Fig. 1, comprises a dielectric shell 10 formed of ethyl cellulose, a base charge 11 of pentaeryth ritoltetranitrate, a priming charge 12 of diazodinitrophenol, an ignition composition 13 of diazodinitrophenolpotassium chlorate, a plastic ignition plug 14 of ethyl cellulose, a semi-conductive plug 15 and a sealing plug 16 of ethyl cellulose. In a modification, Fig. 2, the shell 20 is formed from cellulose acetate and a delay fuze element 21, consisting of a dielectric tube containing a barium peroxide silenium composition, is provided. The base of the semi-conductive ignition plug 25 is coated with a dielectric film 26 of nitrocellulose lacquer and pressed upon a lead styphnate ignition composition 24 ; the shell being closed by a cellulose acetate sealing plug 27. In a second modification, Fig. 3 (not shown), the shell 30 has a portion of reduced inside diameter and is formed of cellulose acetate and closed by a like plug 33. The ignition plug 32 is formed from graphite and rubber and rests upon the shoulder 31 of the shell. In a third modification, Fig. 4 (not shown), a plastic sleeve 41 is disposed about the lower portion of a stepped plug 40 so as to space the upper portion of larger diameter from the wall of the shell. In a fourth modification, Fig. 5 (not shown), the lower portion of the ignition plug is dipped in a dielectric lacquer solution and a bead of ignition composition 13 is disposed about the bridge wire. In a fifth modification, Fig. 6, a plastic ring 61 is fitted about the plug 60 as shown and a bead of ignition composition 13 is again disposed about the bridge wire. The bridge wire is about 0À002 of an inch in diameter and preferably made from a nickel-chromium alloy. The shells may be made from rubber, fibre or tough cellulosic esters and ethers such as cellulose acetate, cellulose acetate.-butyrate and ethyl cellulose. Again the shell may be made from vinyl chloride, vinyl chloride-acetate, polystyrene, acrylic polymers or phenol aldehydes and melamine type resins. Alternatively a metal shell could be provided with a dielectric coating, layer or casing. The lead wires may be made of copper or iron and tinned, if so desired, and may be insulated with cotton servings, rubber or plastic material. The dielectric spacing body may be made of cardboard, paper fibreboard, rubber or plastic material. The ignition plug may be made from aluminium powder or conductive carbon ; the conductive particles being bonded together by a natural or synthetic wax, rubber, rubber-like material, resinous material or sulphur. The base charge may be formed from pentaerythritol tetranitrate, cyclonite, tetryl, trinitrotoluene &c. and may be cast or pelleted as well as pressed. The priming charge may be omitted provided a suitable base charge is used. Any primary explosive or mixture may be used such as diazodinitrophenol-potassium chlorate, lead azide, lead styphnate and mercury fulminate and any known ignition composition may be used such as finely divided diazodinitrophenolchlorate mixture, fulminates, lead- or tinsilenium mixtures &c. The ignition assemblies may employ cavity ignition plugs, matchheads or loose ignition charges. The shell may be sealed by more than one sealing layer or a single seal such as a rubber sealing plug or a cast or moulded resin plug used. U.S.A. Specification 2,658,451 is referred to.