Electric detonators

Only relatively few compounds can act as primary explosives and still meet the restrictive military and industrial requirements for reflabiUty, ease of manufacture, low cost, compatibiUty, and long-term storage stabiUty under adverse environmental conditions. Most initiator explosives are dense, metaHoorganic compounds. In the United States, the most commonly used explosives for detonators include lead azide, PETN, and HMX. 2,4,6-Triamino-l,3,5-triuitrobenzene (TATB) is also used in electric detonators specially designed for use where stabiUty at elevated temperatures is essential. 

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

Magnet Fuse (pronounced Fuzee). A medium power electric detonator, invented in 1854 by Abel, which was fired electrically. The original fuze contd a priming mixt of Cu20, Cu2S and K chlorate packed around the exposed wire leads, and a main charge of either mealed pdr or MF. 

Electric detonators are made from aluminium or copper tubes, the latter being for use in coal mines where aluminium may lead to a possibility of ignition of methane/air mixtures. 

A Minimum lag time 6 Minimum excitation time C Maximum excitation time X Minimum firing current for single detonator V Minimum series tiring current Fig. 10.7. Series firing of electric detonators. 

Application time. In firing electric detonators, the time for which the electric current is applied (see p. 112). 

Bridge wire. The fine wire in an electric detonator which is heated by the firing current. 

Electric detonator. A detonator for firing by electric current. The term does not normally include delay detonators. 

The lead salt is used as a minor component in compositions for low-power electric detonators. 

In general, detonation test apparatus consists of a steel tube that is filled with the substance under investigation. One end of the tube is provided with a booster charge consisting of an electric detonator covered by detonative material. The other end is either closed or provided with a witness plate. One type of steel tube apparatus is provided with a velocity probe to record the shock wave velocity as shown in Figure 2.28. 

Explosives are generally detonated with the assistance of initiating devices (initiators) that are activated by external stimulation sources (friction, spark, or flame), and may include (1) primers, (2) detonators, (3) electric detonators, (4) safety fuses, and (5) detonating cord. 

Electric detonators are also used for detonation of high explosive charges. They are similar in design to other types of detonators except for the presence of an electric fusehead consisting of a bridgewire made of chromium and nickel. The bridgewire is covered by a heat-sensitive pyrotechnic mixture protected by varnish insulation. Standard fuseheads have electrical resistance of 1.2 to 1.4 ohms and... 

An explosive lens is used to generate a flat detonation wave. The explosive lens consists of two cone-shaped segments of explosives, an inner cone and an outer cone, which are fitted together as shown in Fig. 9.2. When detonation is initiated by an electric detonator, a booster charge positioned at the top-center of the inner-cone explosive detonates. Then, the inner cone detonates and the detonation wave propa-... 

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