Delay fuse

Black Powder. Black powder is mainly used as an igniter for nitrocellulose gun propellant, and to some extent in safety blasting fuse, delay fuses, and in firecrackers. Potassium nitrate black powder (74 wt %, 15.6 wt % carbon, 10.4 wt % sulfur) is used for military appHcations. The slower-burning, less cosdy, and more hygroscopic sodium nitrate black powder (71.0 wt %, 16.5 wt % carbon, 12.5 wt % sulfur) is used industrially. The reaction products of black powder are complex (Table 12) and change with the conditions of initia tion, confinement, and density. The reported thermochemical and performance characteristics vary greatly and depend on the source of material, its physical form, and the method of determination. Typical values are Hsted in Table 13. 

With the possible exception of delay fuses, any pyrotechnic mixture represents a hazard worthy of report. Although the cause of frequent accidents reviewed in [2], compositions intended to explode or deflagrate are generally outside the field of this work and few are listed. Numerous reviews and specialist texts exist and hundreds of patents appear yearly. The account [1] of the theory and practice of pyrotechnics contains much useful information on the performance and potential hazards of a great variety of oxidant-fuel combinations which burn very rapidly or explosively. Safety measures are found in [2], Other reviews written from a functional viewpoint are found in [3] and [4], Some hazardously incompatible pyrotechnic mixes are reported [5], Detonability of pyrotechnic compositions has... 

Table 1.2 lists the current applications of black powder. In general, as the balance of the ingredients in the composition shifts from the near stoichiometric 75 15 10 mix, the rate of burning decreases but is still fast enough to be of major importance in hrework rockets, delay fuses, igniters and pyrotechnic smokes. 

A length of match or a pressing of delay fuse connects the rocket motor with the payload so that when the motor burns-out the fuse is lit and communicates with an ejection charge of gunpowder which ignites and ejects the stars. 

The shell case can be made from paper or plastic. For a given calibre, the cylindrical shell holds more stars and is the more straightforward to produce, especially when multiple breaks are required. The much revered ten-break shell (yes, it does burst ten times in the sky ) comprises separate compartments, each connected with a delay fuse to give sequential exploding effects during the flight of the shell. Of course. 

Pressed gunpowder delay fuses are initially prepared, the top fuse being charged with 25 mm of powder (for a longer burn time) while the remaining two fuses contain about 18 mm of powder each. 

The gunpowder explodes in a further fraction of a second, the explosion blowing the shell out of the mortar tube in the manner of a shot from a cannon. At the same time a return section of piped match is lit by the explosion, transferring flame back to the top compartment where it reaches the quickmatch placed across the head of the 25 mm pressed delay fuse. 

In this way the amber stars are ignited and ejected while the third, and final, delay fuse is also burning. 

The 40 mm or so of delay fuse burns noisily for several seconds and when the end of the fuse is reached, smoke, flame and hot particles are showered onto the main gunpowder filling which promptly explodes. The explosion creates a pressure pulse which operates over a few thousandths of a second but which is enough to shatter the tube and clay plug and enter the air as a blast wave. 

The larger Roman candles are htted with plastic end-caps in the obvious interest of waterproofing, and the fuses are extended to include a piped match and a delay fuse. Display hreworks are often arranged as fans on a wooden framework (Figure 8.4) or wrapped as bundles with an interconnecting fuse. 

SHELL A hrework designed to be projected from a mortar tube and containing propellant charge, delay fuse, burster and pyrotechnic units. 

For its functioning, remove the safety pin and pull the T-ring vigorously in order to draw the coated wire thru flash compn. This ignites the powder-train delay and about 8 seconds later the delay fuse explodes the blasting cap (Ref 30a, pp 47-8 and Ref 32b,... 

Photoflash Cartridges, M112A1 (l, 2 or 4-Second Delays) Each consists of a cylindrical A1 container (1.57-inches in diam 7.73-in long), filled with photoflash powder (7. 0-oz), a delay fuse contg gasless Ba chromate boron compn and an electric... 

D. T. Zebree, 53, 17514 (1959) Claims an improved delay fuse for igniting primary explosive compositions in detonators squibs. The preferred delay mixture consists of 60% Ba02,... 

D. T. Zebree, 54, 2745 (1960) Claims an initiating device having a delay fuse element a loose ignition mixt (Pb 72.4/Se 27.6% by wt) in contact. Incorporation of 1-5% Si, which increases the heat of combustion of this mixt, compensates for deteriorations which occur in ignition mixts, esp useful for blasting caps ... 

This delay will vary according to the nature of the explosive composition, its particle size, density and conditions of confinement. This principle of burning to detonation is utilized in delay fuses and blasting detonators. 

In 1935 the Italians invaded Abyssinia (Ethiopia) and over 700 tons of mustard gas was shipped for use by the Italian Air Force. Torpedo-shaped 500-lb bombs, with time-delay fuses, were also utilised. These bombs burst about 200 ft above the ground scattering spray over a considerable area. Later, aerial spraying was the preferred method. Groups of 9 to 15 aircraft followed one another so that the liquid issuing from them formed a continuous fog... soldiers, women, children, cattle, rivers, lakes and pastures were drenched continually with this deadly rain. 6... 

Pyrotechnics include illuminating flares, signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, and photo-flash compounds. Pyrotechnics usually are composed of an inorganic oxidizer and metal powder in a binder. Illuminating flares contain sodium nitrate, magnesium, and a binder. Signaling flares contain barium, strontium, or other metal nitrates [1]. 

In the military, delay fuses are complete shell fuses which set off the explosive charge a definite time after impact. 

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