Manufacture of pyrotechnic time delay compositions
A method of manufacturing a pyrotechnic time delay composition includes admixing together a solid oxidizer, a solid fuel and water to form an aqueous slurry. The slurry is transformed into droplets. The droplets are gas-dried to form particles comprising the oxidizer and the fuel, with the particles thus constituting a pyrotechnic delay composition.
1. A method of manufacturing a slow-burning pyrotechnic time delay composition, wherein the method includes:
admixing together, under high shear and in the absence of a sensitizing oxidizer, a solid oxidizer, a solid fuel and water to form an aqueous slurry;
transforming the slurry into droplets; and
gas-drying the droplets to form particles comprising the solid oxidizer and the fuel, with the particles thus constituting the pyrotechnic delay composition.
2. The method according to claim 1 , wherein a surfactant is present during the admixing of the oxidizer, the fuel and the water to form the slurry.
3. The method according to claim 2 , wherein the surfactant is a wetting agent, and is selected from the group consisting of an acrylic ester, a styrene polymer, and an acrylic copolymer.
4. The method according to claim 3 , wherein the wetting agent comprises 0.25% to 4%, by mass, of the slurry.
5. The method according to claim 2 , wherein the surfactant is a rheology modifier and is selected from the group consisting of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose and powdered smectite clay.
6. The method according to claim 5 , wherein the rheology modifier comprises 0.25% to 4%, by mass, of the slurry.
7. The method according claim 1 , wherein the solid oxidizer is barium sulphate, and comprises 24%-54%, by mass, of the slurry.
8. The method according to claim 1 , wherein the fuel is silicon, zinc and/or magnesium and comprises 5%-50% by mass, of the slurry.
9. The method according to claim 1 , wherein the slurry comprises 40% to 80% water by mass.
10. The method according to claim 1 , wherein transforming the slurry into droplets includes atomizing the slurry.
11. The method according to claim 10 , which includes spray drying the slurry, thereby to achieve the atomization of the slurry into droplets and the gas-drying of the slurry droplets.
12. The method according to claim 11 , wherein the atomization of the slurry includes pumping the slurry at a high pressure through an orifice in a nozzle into a heated gas stream.
13. The method according to claim 11 , wherein the atomization of the slurry includes pumping the slurry at a low pressure through an orifice in a two fluid nozzle into a heated gas stream.
14. The method according to claim 11 , wherein the atomization of the slurry includes allowing the slurry to impinge on a rotating disc in the presence of a heated gas stream whereby high-velocity centrifugal forces generated by the rotating disc are used to form droplets in the gas stream.
15. The method according to claim 11 , wherein the gas stream is a heated gas stream so that the gas-drying of the slurry droplets is thus achieved through contact of the slurry droplets with the heated gas stream.
16. The method according to claim 11 , wherein the gas stream is air, which is at a temperature of about 240° C.
17. The method according to claim 16 , wherein the atomization of the slurry is effected in a chamber through which the air passes.
18. The method according to claim 16 , wherein the water in the slurry droplets evaporates over a period of 1 to 40 seconds, forming more or less spherical particles having a moisture content of up to 1%, by mass.
19. The method according to claim 1 , wherein the pyrotechnic time delay composition has a burning rate of about 210 ms/mm.
20. The method according to claim 1 , wherein the gas-drying comprises gas-drying the droplets in heated air.
21. A method of manufacturing a pyrotechnic time delay composition, wherein the method includes:
admixing together a solid oxidizer, a solid fuel and water, in the presence of a wetting agent selected from the group consisting of an acrylic ester, a styrene polymer, and an acrylic copolymer, thereby to form an aqueous slurry;
transforming the slurry into droplets; and
gas-drying the droplets to form particles comprising the oxidizer and the fuel, with the particles thus constituting a pyrotechnic delay composition.
22. The method according to claim 21 , wherein the wetting agent comprises 0.25% to 4%, by mass, of the slurry.