Delay composition

Verzogerungs-bad, n. (Pkotog.) restraining bath. -mine,/, delayed-action mine, -mittel, n. retarding agent, retarder, delayer, -satz, m. (Expl.) delay composition, -ziinder, m. delayed-action fuse. 

Igniters, Incendiaries, Boosters, and Delay Compositions on a Micro Scale by Use of Infrared Spectroscopy , FrankfordArs Rept T-71-6-1 (1971) 8) G.A. St John M. 

Dwiggins, Particle Size Measurement and the Effect of Particle Size on The Burning Time of Chemical Delay Compositions , NAVWEPS 7304... 

Freeman, Particle Size Measurement of Components, of Pyrotechnic Delay Compositions", PATR 4693 (1975)... 

R.H. Weldon J.R. Bentley, The Effect of Humid Storage on the Burning Properties of a Delay Composition Using Manganese as a Fuel , Australian Weapons Research Establishment, TM CPD 127 (1968) 22) P.J. Humphris ... 

Storage Stability of Manganese Delay Compositions , Expls Pyrots (The Franklin Institute Research Laboratories) 5, Nos 2 3 (Feb Mar 1972) 52) W.E. Perkins T.A. Doris,... 

Theoretical Analysis of Resonance Tube , The Singer Company, Final Report KD 72-82 (1972) 58) F.J. Valenta, The State of the Art of Navy Pyrotechnic Delays , Expls Pyrots (The Franklin Institute Research Laboratories) 5, Nos 11 12 (Nov-Dec 1972). See also Ref 144, pp 185—95. See also Some Factors Affecting Burning Rates and Variability of Tungsten and Manganese Delay Compositions , Ref 144, pp 157—83. See also Mil Spec for Tungsten Delay Compositions , MIL-T-23132A (June 1972) 59) C.F. Parrish et al, Radiation... 

A real advance in the construction of delay detonators was made by Eschbach, who introduced delay compositions which evolved so little gas that there was no longer need to vent the detonator. This eliminated risk of pre-ignition of high explosive and also made it possible to provide fully waterproofed assemblies which gave delay times much more regular because of the removal of variable venting effects. Delay detonators of this type have now virtually superseded all others. 

The burning of a column of delay composition takes place by the passage of a reaction front along the column. The temperature profile of this reaction front can be measured by the use of suitable thermocouples and recording instruments. By analysing the shape of the front it can be shown that the reaction is a solid/solid reaction initiated by thermal conduction of heat through the unreacted material. It follows that to obtain reproducible reaction rates there must be (1) constant amount of solid to solid contact and (2) constant thermal conductivity. 

To attain adequate surface contact between the reacting solids it is necessary to use the ingredients in fine condition and to bring them into contact by pressure. To maintain both solid contact and thermal conductivity correct, the density of the column is controlled at a uniform value. The manufacture of satisfactory delay compositions, therefore, entails the provision of suitably sized ingredients followed by adequate mixing and accurate pressing. 

The manufacture of lead elements commences with the filling of a lead tube, probably 1 m long, by tamping in delay composition. This tube is gradually drawn down until it is of the correct external diameter to be a sliding fit into the detonator shell. It is then accurately cut to the lengths required to give the delay times. 

Some delay compositions are difficult to ignite and ordinary fuseheads may not be adequate for this purpose. In such cases special fuseheads are used which commonly contain cerium powder, or some similar additive which burns with the evolution of a large amount of heat. 

In the design of the detonator attention must also be paid to the effects of the liberation of gas which, though small, is still sufficient to require attention. As the speed of the delay composition is affected by pressure, it is necessary that the free space in the detonator should be carefully controlled. Also, the plug which seals the leading wires in place must withstand this pressure for more than the delay period of the detonator. This task is made more difficult by conduction, along the metal walls of the detonator shell, of heat liberated by the fusehead and the delay composition. Plastic plugs in particular are liable to soften and be ejected from the detonator with probable failure of burning of the delay column. 

The spontaneous ignition of the peroxide in (unspecified) tracer-ignition delay compositions is described. 

Plastic Igniter Cord (PIC) is a modern version of quickmatch in which the gunpowder is replaced by a delay composition, consisting essentially of lead dioxide and silicon, while the support material is aluminium or iron wire. A plastic tube encloses the fuse, as in the manner of electrical... 

Boron is virtually unknown in the fireworks industry, but is a widely-used fuel in igniter and delay compositions for military and aerospace applications. 

For "gasless" heat and delay compositions, little external pressure effect is expected. This result, plus the increase in burning rate observed with an increase in loading pressure, can be considered good evidence for the absence of any significant gas-phase involvement in a particular combustion mechanism. 

Source Glasby, J.S., "The Effect of Ambient Pressure on the Velocity of Propagation of Half-Second and Short Delay Compositions," Report No. D.4152, Imperial Chemical Industries, Nobel Division, Ardeer, Scotland. bCompositions were loaded into 10.5 mm brass tubes at a loading pressure of 20,000 p.s.i. 

Delay Composition A general term for a mixture that burns at a seleeted, reproducible rate, providing a time delay between activation and production of the main effect. A fuse containing a core of black powder is an example of a delay. Highly-reproducible delay mixtures are needed for military applications, and much research effort has been put into developing reliable compositions. 

The purpose of a delay composition is obvious - to provide a time delay between ignition and the delivery of the main effect. Crude delays can be made from loose powder, but a compressed column is capable of much more reproducible performance. The burning rates of delay mixtures range from very fast (millimeters/millisec ond) to slow (millimeters /second). 

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