Process for making and filling a PBX composition

Abstract

The invention relates to a cast explosive composition. A process for formulating a homogenous crosslinked polymer bonded explosive composition comprising the steps of: i) forming an admixture of precure castable explosive composition, comprising an explosive material, a polymerisable binder, and a cross linking reagent which comprises at least two reactive groups each of which is protected by a labile blocking group, wherein the labile blocking groups, comprise at least one resonant acoustic mixing stimulus labile linkage, ii) applying resonant acoustic mixing stimulus to the admixture, causing the at least one resonant acoustic mixing stimulus labile linkage to be removed and release said cross linking reagent, to cause the cure process to start. ##STR00001##

Claims

1. A process for filling a munition with a homogenous crosslinked polymer bonded explosive composition, the process comprising: forming an admixture of pre-cure castable explosive composition, comprising an explosive material, a polymerisable binder, and a cross linking reagent which comprises at least two reactive groups each of which is protected by a labile blocking group, wherein the labile blocking group comprises at least one resonant acoustic mixing stimulus labile linkage; filling the munition with the admixture; and applying a resonant acoustic mixing stimulus to the munition causing the at least one resonant acoustic mixing stimulus labile linkage to be removed and release said cross linking reagent, to cause a cure process to start in the munition.

2. The process according to claim 1, wherein the polymerisable binder is selected, such that it will form with the cross linking reagent a compound selected from 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.

3. The process according to 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, and (ammonium dinitramide), ammonium perchlorate, an energetic alkali metal salt, an energetic alkaline earth metal salt, and combinations thereof.

4. The process according to claim 1, wherein the labile blocking group comprises at least two nitro groups or at least one sterically hindered branched chain hydrocarbyl group.

5. The process according to claim 1, wherein the polymerisable binder and cross linking reagent are partially reacted together to provide a partially polymerised binder-cross linking reagent, wherein at least one of the at least two reactive groups of the cross linking reagent is protected by the labile blocking group.

6. The process according to claim 1, wherein the polymerisable binder is selected such that it will from polyurethane.

7. The process according to claim 1, wherein the cross linking reagent comprises a diisocyanate.

8. The process according to claim 7, wherein the diisocyanate labile blocking group B is selected from: NHR.sup.2R.sup.3, wherein R.sup.2 and R.sup.3 are alkyl, alkenyl, branched-chain alkyl, C(O)R.sup.12, aryl, phenyl, or together form a heterocycle, wherein R.sup.12 is alkyl, alkenyl, branched chain alkyl aryl, phenyl, or R.sup.2 and R.sup.3 together form a lactam; or OR.sup.15, O—N═CR.sup.9R.sup.10, wherein R.sup.15 is aryl, phenyl, benzyl, provided that there are at least two nitro group on the ring, and wherein R.sup.9 and R.sup.10 are independently selected from alkyl, alkenyl, branched chain alkyl, aryl, phenyl, provided that at least one of R.sup.9 or R.sup.10 is a branched chain alkyl or aryl, or phenyl.

9. The process according to claim 1, wherein a defoaming reagent is present in a range from 0.01-2 wt %.

10. The process according to claim 1, wherein the process is a batch process.

11. The process according to claim 2, 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, and (ammonium dinitramide), ammonium perchlorate, an energetic alkali metal salt, an energetic alkaline earth metal salt, and combinations thereof.

12. The process according to claim 11, wherein the labile blocking group comprises at least two nitro groups or at least one sterically hindered branched chain hydrocarbyl group.

13. The process according to claim 11, wherein the polymerisable binder and cross linking reagent are partially reacted together to provide a partially polymerised binder-cross linking reagent, wherein at least one of the at least two reactive groups of the cross linking reagent is protected by the labile blocking group.

14. The process according to claim 11, wherein the polymerisable binder is selected such that it will from polyurethane.

15. The process according to claim 14, wherein the cross linking reagent comprises a diisocyanate.

16. The process according to claim 1, wherein a defoaming reagent is present in a range from 0.01-2 wt %.

17. 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 cross linking reagent which comprises at least two reactive groups each of which is protected by a labile blocking group, wherein the labile blocking group comprises at least one resonant acoustic mixing stimulus labile linkage; and initiating a cure process by applying a resonant acoustic mixing stimulus to the admixture, thereby causing the at least one resonant acoustic mixing stimulus labile linkage to be removed and to release said cross linking reagent, wherein the resonant acoustic mixing stimulus has a frequency of less than 200 Hz.

18. The process according to claim 1, wherein the resonant acoustic mixing stimulus has a frequency of less than 200 Hz.

19. The process according to claim 18, wherein the resonant acoustic mixing stimulus has a frequency from 58 Hz to 60 Hz.

20. The process according to claim 11, wherein the diisocyanate labile blocking group B is a blocked isocyanate selected from: NHR.sup.2R.sup.3, wherein R.sup.2 and R.sup.3 are alkyl, alkenyl, branched-chain alkyl, C(O)R.sup.12, aryl, phenyl, or together form a heterocycle, wherein R.sup.12 is alkyl, alkenyl, branched chain alkyl aryl, phenyl, or R.sup.2 and R.sup.3 together form a lactam; or OR.sup.15, O—N═CR.sup.9R.sup.10, wherein R.sup.15 is aryl, phenyl, benzyl, provided that there are at least two nitro group on the ring, and wherein R.sup.9 and R.sup.10 are independently selected from alkyl, alkenyl, branched chain alkyl, aryl, phenyl, provided that at least one of R.sup.9 or R.sup.10 is a branched chain alkyl or aryl, or phenyl.

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 mixing stimulus process

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

(5) Turning to FIG. 1 there is a general prior art scheme 1, for filling a munition 6. The premix formulation 2, is a mixture of the explosive, HTBP polymerisable binder and other processing aids, and optionally a catalyst. The premix formulation 2 is agitated such as by a stirrer 3. A blocked cross linking reagent 4, (either as a solid or dissolved in a minimal aliquot of solvent), is added to the premix to form the precure formulation 5. The blocked cross linking reagent 4 may be a diisocyanate such as IPDI. The resultant precure admixture 5 is thoroughly mixed and is transferred to a munition 6 or mould (not shown) for later insertion into a munition. The munition 6 when filled with the precure 5 is exposed to heat, which removes the thermally labile blocking group on the blocked cross linking reagent 4, furnishing 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, optionally 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 a cross linking reagent with at least two labile blocking groups 14, are added to the premix to form the precure composition 15. The cross linking reagent 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 mixing 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 mixing energy on the precure composition 15, ensures that the composition is thoroughly mixed to a homogenous state, the continued action of resonant acoustic mixing energy causes the labile blocking groups to be removed and release the cross linking reagent into the composition 15. The further action of the resonant acoustic mixing energy causes the released cross linking reagent to mix homogenously and concomitantly react with the HTPB polymerisable binder.

(8) During the resonant acoustic mixing 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 mixing 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 mixing stimulus 27 provides mixing and assists with starting the cure process.

(11) The action of resonant acoustic mixing energy on the precure composition ensures that the composition is thoroughly mixed to a homogenous state, the continued action of resonant acoustic mixing energy causes the labile blocking groups to be removed and release the cross linking reagent into the composition. The further action of the resonant acoustic mixing energy causes the released cross linking reagent to mix homogenously and concomitantly react with the HTPB polymerisable binder.

(12) 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. The munition 26 may additionally be subject to resonant acoustic mixing to ensure homogeneity.

(13) It should be appreciated that the compositions of the invention are capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described above.