Resonant acoustic mixing (RAM) of an explosive composition

Abstract

The invention relates to a cast explosive composition, particularly to a pre-cure castable explosive composition comprising an explosive material, a polymerisable binder, a microencapsulated cross linking reagent, said microencapsulated cross linking reagent, comprising a cross linking agent encapsulated in a microcapsule. Providing a process for formulating a homogenous crosslinked polymer bonded explosive composition comprising the steps of: i) forming an admixture of pre-cure castable explosive composition, said composition comprising an explosive material, a polymerisable binder, a microencapsulated cross linking reagent, said microencapsulated cross linking reagent, comprising a cross linking reagent encapsulated in a microcapsule;
wherein the microcapsule, comprises at least one shell wall polymer, wherein the microcapsule's shell wall polymer comprises at least one resonant acoustic stimulus labile linkage, ii) applying resonant acoustic stimulus to the admixture, causing the microcapsule to rupture and release said cross linking reagent, to cause the cure process to start.

Claims

1. A process for formulating a homogenous crosslinked polymer bonded explosive composition, the process comprising: forming an admixture of a pre-cure castable explosive composition, said composition comprising an explosive material, a polymerisable binder, and a microencapsulated cross linking reagent, said microencapsulated cross linking reagent comprising a cross linking reagent encapsulated in a microcapsule, wherein the microcapsule comprises at least one shell wall polymer, wherein the microcapsule's shell wall polymer comprises at least one resonant acoustic stimulus labile linkage; wherein applying a resonant acoustic stimulus to the admixture causes the microcapsule to rupture and release said cross linking reagent.

2. The process according to claim 1, comprising: applying a resonant acoustic stimulus to the admixture, thereby causing the microcapsule to rupture and release said cross linking reagent; and filling a munition with the admixture.

3. A process for filling a munition with a homogenous crosslinked polymer bonded explosive composition, the process comprising: forming an admixture of a pre-cure castable explosive composition, said composition comprising an explosive material, a polymerisable binder, and a microencapsulated cross linking reagent, said microencapsulated cross linking reagent comprising a cross linking reagent encapsulated in a microcapsule, wherein the microcapsule, comprises at least one shell wall polymer, wherein the microcapsule's shell wall polymer comprises at least one resonant acoustic stimulus labile linkage; filling the munition with the admixture; and applying a resonant acoustic stimulus to the munition, thereby causing the microcapsule to rupture and release said cross linking reagent.

4. The process according to claim 1, wherein the polymerisable binder is selected such that it will form with the cross linking reagent one or more of: a polyurethane, a cellulosic material, a polyester, a polybutadiene, a polyethylene, a polyisobutylene, polyvinyl acetate (PVA), chlorinated rubber, an epoxy resin, a two-pack polyurethane system, alkyd/melanine, a vinyl resin, an alkyd, a butadiene-styrene block copolymer, polyNIMMO (poly(3-nitratomethyl-3-methyloxetane)), polyGLYN (poly glycidyl nitrate), a glycidyl azide polymer (GAP), and blends, copolymers and/or combinations thereof.

5. The process according claim 1, wherein the explosive material is selected from RDX (cyclo-1,2,3-trimethylene-2,4,6-trinitramine, Hexogen), HMX (cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine, Octogen), FOX-7 (1,1-diamino-2, 2-dinitroethene), TATND (tetranitro-tetraminodecalin), FINS (hexanitrostilbene), TATB (triaminotrinitrobenzene), NTO (3-nitro-1,2,4-triazol-5-one), HNIW (2,4,6,8,10,12-hexanitrohexaazaisowurtzitane), GUDN (guanyldylurea dinitride), picrite (nitroguanidine), an aromatic nitramine, ethylene dinitramine, nitroglycerine, butane triol trinitrate, pentaerythritol tetranitrate, DNAN (dinitroanisole), TNT (trinitrotoluene), an inorganic oxidiser, ADN (ammonium dinitramide), ammonium perchlorate, an energetic alkali metal salt, an energetic alkaline earth metal salt, and combinations thereof.

6. The process according to claim 1, wherein the at least one shell wall polymer is selected from polyurethane, a cellulosic material, cellulose acetate, a polyester, a polybutadiene, a polyethylene, a polyisobutylene, polyvinyl acetate (PVA), chlorinated rubber, an epoxy resin, a two-pack polyurethane system, alkyd/melanine, a vinyl resin, an alkyd, a butadiene-styrene block copolymer, polyNIMMO (poly(3-nitratomethyl-3-methyloxetane)), polyGLYN (poly glycidyl nitrate), a glycidyl azide polymer (GAP), and blends, copolymers and/or combinations thereof.

7. The process according to claim 3, wherein the microcapsule shell wall polymer and the polymerisable binder are selected from substantially the same polymer.

8. The process according to claim 1, wherein the resonant acoustic stimulus labile linkage is selected from acetals, blocked isocyanates, and diels alder linkages.

9. The process according to claim 8, wherein the blocked isocyanates are selected from aromatic heterocycles, secondary amines, substituted phenols, oximes, and amides.

10. The process according to claim 2, wherein causing the microcapsule to release said cross linking reagent is further caused by applying at least one further chemical stimulus and/or one further physical stimulus.

11. A process for filling a munition with a homogenous crosslinked polymer bonded explosive composition, the process comprising: filling the munition with a pre-cure castable explosive composition, said composition comprising an explosive material, a polymerisable binder, and a cross linking reagent; and applying a resonant acoustic stimulus to the munition.

12. The process according to claim 11, wherein the reagents of the pre-cure are transferred into the munition layerwise, such that the resonant acoustic stimulus causes homogenous mixing to form an admixture and concomitantly causes the crosslinking reagent to mix with the polymerisable binder to cause a cure process to start.

13. A continuous filling process for filling a plurality of munitions with a homogenous crosslinked polymer bonded explosive composition, the process comprising: forming a pre-cure castable explosive composition by providing a continuous feed of an explosive material, a polymerisable binder, and a cross linking reagent into a continuous resonant acoustic mixer; applying a resonant acoustic stimulus to the continuous resonant acoustic mixer to form the homogenous crosslinked polymer bonded explosive composition; and filling the plurality of munitions with the homogenous crosslinked polymer bonded explosive composition.

14. The process according to claim 3, wherein applying the resonant acoustic stimulus comprises applying the resonant acoustic stimulus in a frequency range of less than 200 Hz.

15. The process according to claim 14, wherein the frequency range is from 58 Hz to 60 Hz.

16. The process according to claim 3, wherein the polymerisable binder is selected such that it will form with the cross linking reagent one or more of: a polyurethane, a cellulosic material, a polyester, a polybutadiene, a polyethylene, a polyisobutylene, polyvinyl acetate (PVA), chlorinated rubber, an epoxy resin, a two-pack polyurethane system, alkyd/melanine, a vinyl resin, an alkyd, a butadiene-styrene block copolymer, polyNIMMO (poly(3-nitratomethyl-3-methyloxetane)), polyGLYN (poly glycidyl nitrate), a glycidyl azide polymer (GAP), and blends, copolymers and/or combinations thereof.

17. The process according claim 3, wherein the explosive material is selected from RDX (cyclo-1,2,3-trimethylene-2,4,6-trinitramine, Hexogen), HMX (cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine, Octogen), FOX-7 (1,1-diamino-2, 2-dinitroethene), TATND (tetranitro-tetraminodecalin), FINS (hexanitrostilbene), TATB (triaminotrinitrobenzene), NTO (3-nitro-1,2,4-triazol-5-one), HNIW (2,4,6,8,10,12-hexanitrohexaazaisowurtzitane), GUDN (guanyldylurea dinitride), picrate (nitroguanidine), an aromatic nitramine, ethylene dinitramine, nitroglycerine, butane triol trinitrate, pentaerythritol tetranitrate, DNAN (dinitroanisole), TNT (trinitrotoluene), an inorganic oxidiser, ADN (ammonium dinitramide), ammonium perchlorate, an energetic alkali metal salt, an energetic alkaline earth metal salt, and combinations thereof.

18. The process according to claim 3, wherein the at least one shell wall polymer is selected from polyurethane, a cellulosic material, cellulose acetate, a polyester, a polybutadiene, a polyethylene, a polyisobutylene, polyvinyl acetate (PVA), chlorinated rubber, an epoxy resin, a two-pack polyurethane system, alkyd/melanine, a vinyl resin, an alkyd, a butadiene-styrene block copolymer, polyNIMMO (poly(3-nitratomethyl-3-methyloxetane)), polyGLYN (poly glycidyl nitrate), a glycidyl azide polymer (GAP), and blends, copolymers and/or combinations thereof.

19. The process according to claim 3, wherein the resonant acoustic stimulus labile linkage is selected from acetals, blocked isocyanates, and diels alder linkages.

20. The process according to claim 3, wherein causing the microcapsule to release said cross linking reagent is further caused by applying at least one further chemical stimulus and/or one further physical stimulus.

Description

(1) An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings of which:—

(2) FIG. 1 shows a prior art schematic of the fill of an HE ammunition process

(3) FIGS. 2a and 2b shows a schematic of the fill of an HE ammunition using a resonant acoustic stimulus process

(4) FIG. 3 shows a continuous filling process arrangement.

(5) Turning to FIG. 1 there is a general scheme 1, for filling a munition 6. The premix composition 2, is a mixture of the explosive, HTBP polymerisable binder and other processing aids, and optionally a catalyst. The premix composition 2 is agitated such as by a stirrer 3. Microcapsules comprising a cross linking reagent 4, are added to the premix to form the precure formulation. The cross linking reagent (not shown) may be a diisocyanate such as IPDI. The resultant precure admixture 5 is thoroughly mixed and is transferred to a munition 6 or mould or pot for later insertion into a munition (not shown). The munition 6 when filled with the precure 5 may then be exposed to an external stimuli, such as heat, which ruptures the microcapsules 4, causing release of the cross linking reagent. The cross linking reagent and HTPB polymerisable binder may then polymerise and form a polymer bonded explosive 7.

(6) Turning to FIGS. 2a and 2b there is a general scheme 11, for filling a munition 16, optional via filling funnel 19 (FIG. 2b). The premix formulation, is a mixture of the explosive, HTBP polymerisable binder other processing aids, optionally a catalyst and microcapsules comprising a cross linking reagent 14, are added to the premix to form the precure composition 15. The cross linking reagent (not shown) may be a diisocyanate such as IPDI. The resultant precure admixture 15 in the munition is located on a platform 13, which is in mechanical contact with a resonant acoustic stimulus source 17 to provide resonance at a frequency of 58 to 60 Hz. In order to secure the munitions 16 in place, they may be placed in a rack system 12, which may comprise further restraints 12a, 12b to secure the munition to the rack 12 and platform 13 to ensure that the acoustic, that is vibrational energy, is transferred from the source 17 to the munitions 16 and precure composition 15.

(7) The action of resonant acoustic energy on the precure composition 15, ensures that the composition is thoroughly mixed to a homogenous state, the continued action of resonant acoustic energy causes the microcapsules to rupture and release the cross linking reagent within said microcapsule. The further action of the resonant acoustic energy causes the released cross linking reagent to mix homogenously and concomitantly react with the HTPB polymerisable binder.

(8) During the resonant acoustic stimulus process the application of a vacuum 18, may assist to degas the curing composition, by removing trapped gases and volatiles, to reduce the instances of voids. The mixing arrangement may require additional thermal control, such as external heating or cooling to control the temperature of the reaction.

(9) Alternatively the composition ingredients may be dosed to a large batch mixing vessel, either volumetrically or by mass. The mixing vessel is then brought into mechanical contact with a resonant acoustic stimulus source 17 to provide a batch cure process. The resulting curing composition may then be transferred to munitions or pots, in the standard manner.

(10) Turning to FIG. 3 there is provided a continuous resonant acoustic mixer system 21, comprising a mixer 28, which is primed with the components via continuous inlet feeds 24. A resonant acoustic stimulus 27 provides mixing and assists with starting the cure process. The curing admixture is then transferred via a pipe 29 to fill the munition 26. The filling may be carried out volumetrically, by mass and optionally under a vacuum.