Fuse (explosives)

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"Fuze" redirects here. For other uses, see Fuze (disambiguation).

In an explosive, pyrotechnic device or military munition, a fuse (or fuze) is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately. However, when being specific (and in particular in a military context), the term fuse describes a simple pyrotechnic detonating device, like the cord on a firecracker, whereas the term fuze is used to indicate a more sophisticated ignition device incorporating mechanical and/or electronic components e.g. a proximity fuze for an M107 artillery shell, magnetic/acoustic fuze on a sea mine, spring-loaded grenade fuze[1][2][3], pencil detonator or anti-handling device.

A burning fuse (visco)
A burning fuse (visco)
A fuze for an artillery shell
A fuze for an artillery shell

Contents

[edit] History

The simplest form of fuse is the burning fuse, believed to date back to the 10th century and originating in China, this simple fuse consisted of lightweight paper filled with loose gunpowder, and served as a means of delaying ignition in fireworks. This simple form of burning fuse can still be found today in many modern pyrotechnics. A version of this simple fuse is called visco fuse, and consists of the burning core coated with wax or lacquer for durability and water resistance. The commercial and military version of a burning fuse referred to as safety fuse (invented by William Bickford) is a textile tube filled with combustible material and wrapped to prevent external exposure of the burning core. Safety fuses are used to initiate the detonation of explosives through the use of a blasting cap.

[edit] Fuses

Modern day safety fuses are often used in mining and military operations, to provide a time-delay before ignition, and they more often than not are used to initiate an explosive detonator, thereby starting an explosive chain reaction to detonate a larger more stable main charge. Safety fuses are typically colored black (military) or fluorescent orange (commercial) to distinguish them from detonating cords such as Primacord, which are brightly colored or transparent.

[edit] Usage

Fuses are found in fireworks, model cannons, antique smoothbore firearms, some improvised explosive devices and many forms of pyrotechnics.

[edit] Types

[edit] Burning Fuses

  • A slow match is a very slow-burning fuse consisting of a hemp or cotton rope saturated with an oxidizer such as potassium nitrate. Slow matches are used as a source of fire for manually lighting other devices, such as matchlock guns, or fuses on black powder cannons. Before percussion caps, slow matches were most suitable for use around black powder weapons because it could be roughly handled without going out, and only presented a small glowing tip instead of a large flame that risked igniting powder supplies nearby.
  • Today's punks (wood splints covered with ground plant pith or dung and then saturated with nitrate) used for lighting consumer fireworks are a type of slow match.
  • A Black match is a type of fuse consisting of cotton string coated with a dried slurry of black powder and glue. This acts as a simple pass-fire, and was used to fire ancient cannons. They are used today in fireworks construction.
  • A quick match or piped match is a type of black powder fuse that burns very quickly, some hundreds of feet per second. They consist of black matche covered with a loose paper wrap (pipe). When lit, the flame propagates quickly down the paper pipe from the hot gases produced by the burning powder. Quick matches are used in professional fireworks displays to pass fire nearly instantly between devices that must be physically separated while firing simultaneously, such as a finale rack. Devices which should fire in sequence can be branched from a single master fuse, consisting of quick match spliced onto Visco fuses of various length for time delays.
  • A visco fuse has a core of black powder with one or more textile overwraps, The outer layers may be coated with wax or nitrocellulose lacquer for water resistance. These fuses are widely used in modern pyrotechnics because they burn at a uniform rate, with an easily visible external flame. Depending on their outer treatment, visco fuses are water resistant and the better quality can burn reliably underwater once lit, since the black powder core provides both its own fuel and oxidant.
  • A safety fuse consists of a black powder core in a textile tube, covered with asphaltum or other waterproofing agent, and having an outer wrapper of tough textile or plastic. They are made in a standard diameter designed to be crimped into blasting caps.[4] Once ignited, safety fuses will burn underwater, and have no external flame that might ignite methane or other fuels such as might be found in mines or other industrial environments. Safety fuses are manufactured with specified burn times per 30 cm, e.g. 60 seconds, which means that a length of fuse 30 cm long will take 60 seconds to burn. Manufacturers warn that although every effort is made to insure uniform burn times, safety fuses are subject to variation depending on conditions and should be used with adequate safety margins.
  • An Igniter Safety Fuse Electric (ISFE) lights a main fuse or device when activated by an electrical current. They typically consist of a pair of wires leading to a thin resistance wire that heats when current is applied. The resistance wire is covered by a bit of pyrotechnic composition that ignites from the wire heating, providing enough fire to reliably ignite the main fuse via a mechanical connection, or the device directly. Estes model rocket motors are lit by a type of electric match. Large fireworks displays are launched with complex timing sequences using a computer that energizes electric matches connected to the individual device fuses.
  • A flying fish fuse (bumblebees) is an unusual type of component for fireworks. It is made like Visco fuse, but contains a metallic spark composition or other effect instead of black powder. Flying fish can thus perform as a main effect instead of just an initiator. For example, simply lighting a short piece of flying fish on the ground makes it fly through the air, seeming to swim in random directions, while emitting sparks and noise. A aerial shell loaded with many such pieces results in a beautiful myriad of pieces flying and sparking high in the air.
  • A spoolette is a delay fuse consisting of a hollow wooden dowel rammed full of black powder. A spoolette is glued into the wall of a fireworks shell and ignited by the lift charge that launches the shell into the air. The spoolette, after a delay that allows the shell to reach its top of trajectory, ignites the shell's main effect(s). The tough wood construction ensures that the fuse burns reliably despite the explosive force and acceleration of the launch.
  • The saucisson was an early form of fuse.

[edit] Munition fuzes

An assortment of fuzes for artillery and mortar shells

Most countries use the 'z' spelling to distinguish between simple burning fuses and more complicated munition fuzes. Examples of both spellings can be found.

A fuze refers to a device used in munitions which is designed to detonate, or to set forces into action to ignite, detonate or deflagrate, the charge (or primer) under specified conditions.

[edit] Types

Types of fuzes include:

  • time fuzes detonate after a set period of time by using one or more combinations of mechanical, electronic, pyrotechnic or even chemical timers. Depending on the technology used, the device may detonate (or render itself safe without detonation) some minutes, hours, days, or even months after being deployed.
  • contact detonators or point detonating fuzes detonate immediately on impact with the target.
  • proximity fuzes cause a missile warhead or other munition (e.g. air-dropped bomb or sea mine) to detonate when it comes within a certain pre-set distance of the target, or vice versa. Proximity fuzes utilize sensors incorporating one or more combinations of the following: radar, active sonar, passive acoustic, infrared, magnetic, photoelectric, seismic or even television cameras. These may take the form of an anti-handling device designed specifically to kill or severely injure anyone who tampers with the munition in some way e.g. lifting or tilting it. Regardless of the sensor used, the pre-set triggering distance is calculated such that the explosion will occur sufficiently close to the target that it is either destroyed or severely damaged.
  • remote detonators use wires or radio waves to remotely command the device to detonate.
  • barometric fuzes cause a bomb to detonate at a certain pre-set altitude above sea level by means of an radar, barometric altimeter or and infrared rangefinder.

[edit] Usage

Many weapons have fuzing systems to ensure that they do not initiate (explode) prematurely. In most cases the munition has to travel some distance or wait for a period of time (via clockwork, electronic or even a chemical delay) before it can detonate.

In modern artillery shells, most fuzes incorporate several safety features to prevent a fuze arming before it leaves the gun barrel. These safety features may include arming on "set-back" or by centrifugal force, and often both operating together. Set-back arming uses the inertia of the accelerating artillery shell to remove a safety feature as the projectile accelerates from rest to its in-flight speed. Rotational arming requires that the artillery shell reach a certain rpm before centrifugal forces cause a safety feature to disengage or move an arming mechanism to its armed position - artillery shells are fired through a rifled barrel, and so spin during flight.

In other cases the bomb, mine or projectile has a fuze that prevents accidental initiation eg stopping the rotation of a small propellor so that the striker-pin cannot hit the detonator even if the weapon is dropped on the ground). These types of fuze operate with aircraft weapons, where the weapon may have to be jettisoned over friendly territory to allow a damaged aircraft to continue to fly. The crew can choose to jettison the weapons safe by dropping the devices with safety pins still attached, or drop them live by retaining the safety pins as the weapons leave the aircraft.

Aerial bombs and depth charges can be nose and tail fuzed using different detonator/initiator characteristics so that the crew can choose which effect fuze will suit target conditions that may not have been known before the flight. The arming switch is set to one of safe, nose, or tail at the crew's choice.

Base fuzes are also used by artillery and tanks for shells of the 'squash head' type. Some types of armour piercing shells have also used base fuzes, as have nuclear artillery shells.

There also exist more complicated integrated fuzing and firing systems, typically used in missiles and special weapons.

[edit] See also

[edit] References

  1. ^ Grenade fuze - Patent 4063514
  2. ^ DUAL SAFETY GRENADE FUZE - Patent 3618522
  3. ^ Ammunition Peculiar Equipment (APE) 1955 Grenade Fuze Tester MIL-STD-398 Test.
  4. ^ DuPont Blaster's Handbook, Fifteenth Edition, Wilmington, Delaware, E.I. DuPont de Nemours and Company, Inc., 1969, pp 97-99

[edit] External links

[edit] Gallery of Fuzes

Fuzes fitted to M107 155mm artillery shells

Mk 53 Proximity fuze used in artillery shells

British No. 63 Mk I Time and Percussion fuze, circa 1915 - used in shrapnel shells

British No. 100 Graze Fuze for high-explosive shell, World War I.

Hotchkiss base percussion fuze for artillery shells, circa World War I

British No. 25 time fuze Mk IV, 1914, used for star shells

British Time Fuze No. 31, World War I, used in trench mortars

British Percussion Fuze No. 110 Mk III, World War I, used in trench mortars

British No. 131 D.A. (Direct Action) Impact Fuse, Mk VI, World War I, used in anti-aircraft artillery

Percussion fuze for an artillery shell

British No. 16 D Mk IV N Base percussion fuze, circa 1936

British No. 45 P Direct Action Impact Fuze, World War I, used in howitzer shells

Soviet pull-fuze designed for booby-trap purposes. Detonator assembly is inserted into explosives

Alternative design of Soviet pull-fuze, usually connected to a tripwire

Soviet pressure fuze for boobytrap purposes e.g. victim steps on loose floorboard with fuze (connected to TNT explosives) concealed underneath