Abridgewire orbridge wire, also known as ahot bridge wire (HBW), is a relatively thinresistance wire used to set off apyrotechnic composition serving aspyrotechnic initiator. By passing ofelectric current it isheated to a high temperature that starts theexothermicchemical reaction of the attached composition. After successful firing, the bridgewire melts, resulting in anopen circuit.
Usually a thinnichrome wire is used. Some applications also useplatinum-silver alloy; other bridgewire materials in use areplatinum,gold,silver,tungsten, etc. Care has to be taken when selecting the material as it is in direct contact with the pyrotechnic composition and should not undergo corrosion in such conditions. Another material, able to actively release chemical energy, isPyrofuze,aluminium wire clad withpalladium; when being heated it undergoes strongly exothermic reaction as the molten metals form an alloy. A variant with the same function consists of laminated thin alternate layers of aluminium andnickel.Carbon bridge is a thin spot ofcolloidalgraphite used as the bridgewire. Some variants use a conductive pyrotechnic composition as the resistive material. Inamateur rocketry, grossly overloaded low wattage metal filmresistors and 0805Surface-mount technology resistors are also used.[1]
A shallow notch cut into the center of the bridgewire promotes gross localized overheating instead of homogeneous heating of the entire bridgewire. This may improve the bridgewire performance in some applications.
Bridgewires are used in diverse applications; to triggerdetonators,electric matches,squibs, electricblasting caps,pyrotechnic fasteners, and more. Bridgewires dipped in a suitable pyrotechnic composition (pyrogen) are known aselectric matches. Pyrogens with content ofmagnesium allow reaching very high combustion temperatures.
Devices using bridgewires, whether for initiating an explosion ("electroexplosive") or for nonexplosive purposes, are calledbridge wire actuated devices (BWAD).[2]
Bridgewires, especially connected to longer cables, may be susceptible to initiation by currents induced by externalelectromagnetic fields.[3]
By passing an extremely high amount of electric current through the bridgewire, it gets rapidly vaporized, causing a smallexplosion. This is exploited inexploding-bridgewire detonators (EBWs), used for very safe and highly precise initiation of explosives, e.g. innuclear weapons.