CAST EXPLOSIVE COMPOSITION

Abstract

The invention relates to a cast explosive composition comprising a polymer-bonded explosive and a defoaming agent, and to a process for reducing the number and/or total volume of voids in a cast explosive composition comprising the steps of: combining a polymer-bonded explosive and a defoaming agent; and casting the explosive composition. The defoaming agent may be used for reducing the number and/or total volume of voids in a cast explosive composition and the cast explosive composition may be used in an explosive product.

Claims

1-16. (canceled)

17. A method for producing a cast and cured explosive composition, the method comprising vacuum casting a castable explosive composition comprising a polymer-bonded explosive in admixture with 0.01-2 wt % of a silicone-free defoaming agent and wherein said castable explosive composition contains entrained bubbles therein which become substantially removed by coalescence and egress, as facilitated by the silicone-free defoaming agent, during casting; and curing the cast; wherein said polymer-bonded explosive comprises an explosive and a polymer binder; and wherein said cast and cured explosive composition possesses a substantial absence of voids, wherein said silicone-free defoaming agent possesses the characteristic of being surface active at interfaces between bubbles and the polymer-bonded explosive and facilitating the coalescence and egress of bubbles.

18. The method according to claim 17, wherein the defoaming agent is present in an amount of 0.03-2 wt %.

19. The method according to claim 17, wherein said defoaming agent is present in an amount of 0.5 to 2 wt %.

20. The method according to claim 17, wherein said defoaming agent is present in an amount of 0.25 to 1 wt %.

21. The method according to claim 17, wherein said defoaming agent is present in an amount of 0.5 to 1 wt %.

22. The method according to claim 17, wherein said defoaming agent is present in an amount of 0.25 to 2 wt %.

23. The method according to claim 17, wherein the polymer-bonded explosive and the defoaming agent are combined in the presence of a solvent.

24. The method according to claim 17, wherein the polymer-bonded explosive and the defoaming agent are combined in the absence of a solvent.

25.-27. (canceled)

28. The method according to claim 17, wherein the defoaming agent comprises a combination of silicone-free defoaming agent with a polysiloxane.

29. The method according to claim 17, wherein said polymer binder is selected from polyurethane, cellulosic materials such as cellulose acetate, polyesters, polybutadienes, polyethylenes, polyisobutylenes, PVA, chlorinated rubber, epoxy resins, two-pack polyurethane systems, alkyd/melanine, vinyl resins, alkyds, self-crosslinking acrylates, butadiene-styrene block copolymers, polyNIMMO, polyGLYN, GAP, and blends, copolymers, and combinations thereof.

30. The method according to claim 17, wherein said polymer binder comprises polyurethane.

31. The method according to claim 30, wherein said polyurethane includes a hydroxyterminated polybutadiene.

32. The method according to claim 17, wherein said explosive is selected from RDX, HMX, FOX-7, TATND, HNS, TATB, NTO, HNIW, GUDN, picrite, tetryl, ethylene dinitramine, nitroglycerine, butane triol trinitrate, pentaerythritol tetranitrate, DNAN trinitrotoluene, ammonium nitrate, ADN, ammonium perchlorate, energetic alkali metal salts, energetic alkaline earth metal salts, and combinations thereof.

33. The method according to claim 17, wherein said explosive composition further comprises a metal powder.

34. The method according to claim 33, wherein said metal powder is selected from aluminum, magnesium, tungsten, alloys of these metals, and combinations thereof, in admixture with the polymer-bonded explosive.

35. The method according to claim 17, wherein said explosive comprises RDX.

36. The method according to claim 17, wherein said explosive comprises RDX and said polymer binder comprises polyurethane.

37. The method according to claim 36, wherein said RDX is in an amount in the range of about 75-95 wt % and said polyurethane binder is in an amount in the range of about 5-25 wt %.

38. The method according to claim 17, wherein said silicone-free defoaming agent is present in an amount of about 1 wt %.

39. The method according to claim 17, wherein said silicone-free defoaming agent is an alkoxylated alcohol.

40. The method according to claim 17, wherein said vacuum casting is conducted under a vacuum at a pressure of less than 10 mm Hg.

Description

EXAMPLES

Example 1

[0040] A series of commercially available defoaming agents were cast and cured with Rowanex 1100 (88 wt % RDX and 12 wt % polyurethane agent). Curing occurred over 5 days at 65? C. 105 mm and 155 mm shells prepared using the resulting composition were found to have no detectable voids, and no adverse effect on the chemical or mechanical properties of the polymer-bonded explosive were observed. Table 1 below illustrates the effect of binder type and level on the viscosity and density of the composition.

TABLE-US-00001 TABLE 1 Den- Den- Dos- sity - sity - % age Vis- Vacuum Air TMD.sup.? (wt cosity Cast Cast (air 1. Defoaming Agent* %) (cps).sup.# (g/cm.sup.3) (g/cm.sup.3) cast) No Additive 0.12 1.608 1.608 99.3 Solution of foam-destroying 1.0 0.035 1.608 1.602 99.6 polymers and polysiloxanes in isoparaffin solvent (BYK 088) Solution of silicone-free 1.0 0.033 1.612 1.606 99.9 foam-destroying polymers in Alkylbenzene/ methoxypropylacetate 12/1 (BYK A500) Solution of foam-destroying 0.1 0.12 1.614 1.619 99.6 polysiloxanes in diisobutylketone (BYK 066N) Solution of foam-destroying 0.5 0.063 1.618 1.608 99.6 polysiloxanes in diisobutylketone (BYK 066N) Solution of foam-destroying 1.0 0.04 1.620 1.605 99.8 polysiloxanes in diisobutylketone (BYK 066N) Solvent free mixture of 0.1 0.076 1.6 1.6 98.9 foam-destroying polymers silicone free (BYK A535) Solvent free mixture of 0.5 0.07 1.612 1.608 99.6 foam-destroying polymers silicone free (BYK A535) Solvent free mixture of 1.0 0.034 1.59 1.597 99.3 foam-destroying polymers silicone free (BYK A535) Concentrate based on 0.1 0.12 1.605 1.622 100 organosiloxanes plus fumed silica (TEGO MR2132) Concentrate based on 0.5 0.073 1.613 1.609 99.7 organosiloxanes plus fumed silica (TEGO MR2132) Concentrate based on 1.0 0.047 1.594 1.561 97.1 organosiloxanes plus fumed silica (TEGO MR2132) Solvent free, silicone free 0.1 0.133 1.611 1.612 99.6 alkoxylated alcohol (BASF SD23) Solvent free, silicone free 0.5 0.09 1.597 1.597 98.9 alkoxylated alcohol (BASF SD23) Solvent free, silicone free 1.0 0.28 1.623 1.623 100 alkoxylated alcohol (BASF SD23) Solvent free, silicone free 0.1 0.08 1.609 1.610 99.5 triisobutyl phosphate (BASF SD40) Solvent free, silicone free 0.5 0.06 1.598 1.603 99.3 triisobutyl phosphate (BASF SD40) Solvent free, silicone free 1.0 0.07 1.596 1.598 99.4 triisobutyl phosphate (BASF SD40) Dibutylketone only 1.0 1.599 1.598 99.4 Dibutylketone only 0.5 1.597 1.602 99.2 *defoaming agents were procured from BYK Additives and Instruments, a subdivision of Altana; Evonik or BASF .sup.#Viscosity determined at 60? C. .sup.?TMD is the Theoretical Maximum Density of the composition calculated to allow for the intrinsic density lowering effect arising when additives are added. The TMD is the sum of the relative volume of each component as determined from their relative mass within the composition and known density. As a result, the TMD gives a true indication of the density modification arising as a result of a change in the number of voids.

[0041] As can be seen, the presence of each of the defoaming agents at levels above 0.1 wt % reduces the viscosity of the composition making it easier to cast. Further, as the level of defoaming agent is increased to 1.0 wt %, the viscosity of the composition is further reduced.

[0042] The presence of defoaming agent also increases the density, providing an indicator that the number of voids has been reduced. Calculation of the TMD provides a further indicator, as an increase in the TMD relative to that obtained where no additive is present shows that the number of voids in the sample has been reduced relative to the additive free composition.

[0043] It is clear that it is the defoaming agent having a density increasing effect as the addition of dibutylketone only (i.e. solvent only), reduces the density of the composition whether prepared by a vacuum or an air casting technique.

[0044] The data above shows that vacuum casting generally produces compositions of a higher relative density than air casting techniques where defoaming agents are present. Further, vacuum casting techniques generally have a more marked effect upon the density of compositions containing defoaming agents when compared to additive free or solvent only compositions.

[0045] However, even where air casting techniques are used, it is clear that the defoaming agents are acting to reduce the number of voids in the compositions tested as each defoaming agent provides a composition which is either of higher density, or has a higher TMD, than the control compositions including either no additive, or solvent only.

Example 2

[0046] The compatibility of the defoaming agents with the Rowanex 1100 was also tested, and the results set out in Table 2 below.

TABLE-US-00002 TABLE 2 1. Defoaming Agent Compatibility BYK 066N * Pass Solution of foam-destroying polysiloxanes in Pass propylene glycol (BYK 088A) * BYK 088 * Pass BYK A500 * Pass BYK A535 * Pass TEGO MR2132.sup.# Pass BASF SD23 .sup.? Pass BASF SD40 .sup.? Pass * Procured from BYK Additives and Instruments, a subdivision of Altana .sup.#Procured from Evonik .sup.? Procured from BASF

[0047] Compatibility was measured following STANAG 4147 Test 1: Procedure B, at a temperature of 100? C. for 40 hours. All of the defoaming agents tested were found to meet the requirements of this test, and hence to be compatible with the Rowanex 1100 PBX product, as illustrated by the results in the table above which indicate that each of the materials tested evolved less than 1 ml/g of gas for a 5 g sample. No adverse reaction was observed with any of the defoaming agents, although a particularly good compatibility was observed between Rowanex 1100 and BYK A535. Indeed, the use of BYK A535, a solventless defoaming agent, has been found to provide a particularly stable product with acceptable activity in terms of void removal.

Example 3

[0048] The sensitivity of the Rowanex 1100 and defoaming agent mixtures was tested for sensitivity to mechanical impact (Rotter Impact) to determine the relative hazard associated with using the mixture as opposed to the pure PBX product. The results are set out in Table 3.

TABLE-US-00003 TABLE 3 1. Additive Concentration (wt %) F of I None 100 BYK 088 1 130 BYK A500 1 130 BYK 066N 1 130 BYK A535 0.5 102 TEGO MR2132 1 109 BASF SD23 1 112 BASF SD40 1 121

[0049] The test determines the 50% drop height for the test sample. This examines the whole probability of ignition versus stimulus-level relationship. Seven test heights equally spaced on a logarithmic scale are chosen and caps are tested to see if ignitions take place. Results are expressed in terms of Figures of Insensitiveness (F of I) relative to standard RDX. All tests are carried out on samples of ground up material. The Rotter Impact Test method was used to determine the F of I using an LSM Rotter machine.

[0050] The F of I value for all of the Rowanex 1100/defoaming agent samples was found to be greater than or equal to the F of I value for Rowanex 1100 alone. This indicated that the presence of the defoaming agent has no adverse effect on the sensitivity of the PBX to mechanical impact and that as a result the combination products are no more hazardous, and in some cases less hazardous, to use than Rowanex 1100 alone. Without being bound by theory, this may be due to the marginal increase in binder, and resultant reduction in nitramine content because of the presence of the defoaming agent. It is further indicated that the Rowanex 1100/defoaming agent samples are likely to be no more sensitive to ignition than untreated Rowanex 1100.

Example 4

[0051] A series of compositions including RDX were prepared, three of these compositions included defoaming agents.

TABLE-US-00004 TABLE 4 Examples of Polymer-bonded Explosive (PBX) Compositions containing Defoaming Agents PBX with PBX with PBX with 0.1% BYK- 0.5% BYK- 1% BYK- A500 A535 066N PBX Defoamer Defoamer Defoamer Abbreviation Full name Function (wt %) (wt %) (wt %) (wt % DOA Dioctyl Adipate Plasticiser 7.00 6.99 6.96 6.93 HTPB Hydroxyterminated Pre- 4.28 4.28 4.26 4.24 Polybutadiene polymer Lecithin Surfactant 0.30 0.30 0.30 0.30 AO2246 2,2-methylenebis- Anti- 0.10 0.10 0.10 0.10 (4-methyl-6- oxidant tertiary- butylphenol) IPDI Isophorone Curing 0.42 0.42 0.42 0.42 Diisocyanate Agent DBTDL dibutyltin dilaurate Catalyst 0.05 0.05 0.05 0.05 Additive 0.00 0.10 0.50 1.00 RDX* Hexogen Explosive QS QS QS QS Filler *May be present as pure RDX or combined with a plasticiser, for instance in the ratio 94:6 RDX:plasticiser.

[0052] The compositions were prepared using cast and curing processes as described in Example 1 and no voids were detected. No adverse effect on chemical and mechanical properties was observed relative to the defoaming agent free RDX composition.

Example 5

[0053] The following example illustrates a method of preparing PBX compositions of the invention, such as the compositions of Example 4, using a premix. The techniques used would be well known to the person skilled in the art.

[0054] A water-jacketed, vertical mixer fitted with a rotating stirrer blade was used for the preparation of the composition. All mixing was carried out under vacuum at a pressure of less than 10 mm Hg. The compositions of this example were prepared on a 5 Kg scale using the relative proportions of components set out in Example 4 above.

[0055] The premix was prepared from RDX desensitised with water. The water was then driven off using techniques common in the art. The desensitised RDX (94 wt %) was then mixed with DOA plasticiser (6 wt %) to form the premix.

[0056] The mixer was preheated to 60?2? C. and the following ingredients weighed into the mixer in sequential order in relative amounts as described in Example 2 above: [0057] 1. HTPB [0058] 2. DOA [0059] 3. Lecithin [0060] 4. AO 2246 [0061] 5. Premix (first quarter portion, i.e. 25 wt % of total premix to be added)

[0062] The composition was mixed for 15 minutes. The second, third and final quarter portions of premix were then added with 10 minutes of mixing between each addition and after the final addition. The mixer blades and bowl were scraped down to ensure that any unmixed material was transferred to the mixing zone of the bowl and the composition mixed for a further 60 minutes.

[0063] Defoaming agent was then added and the composition mixed until the maximum reduction in viscosity upon addition of the defoaming agent to the composition was observed. In this case mixing was for 25 minutes and viscosity reduction was measured using a torque meter fixed to the mixer, when the torque required to complete the mixing stabilised at a lower level than before the addition of the defoaming agent, the maximum reduction in viscosity is regarded as having been observed.

[0064] The DBTL was added and the composition mixed for 15 minutes, then the IPDI added and the composition mixed for a further 15 minutes. After mixing the viscosity of the composition was recorded using a Brookfield viscometer (60? C.).

[0065] The composition was cast and any excess mixture removed from the shell housings. The shells were placed onto a vibrating table and allowed to vibrate for 5 minutes. The charges were cured for 5 days at 65?2? C.

Example 6

[0066] The following example illustrates a method of preparing PBX compositions of the invention, such as the compositions of Example 4, from a precure. The techniques used would be well known to the person skilled in the art.

[0067] Mixing conditions were as for Example 5. The precure was prepared from the premix described in Example 5 above. To this premix was added all of the components of the composition of Example 5 except for the defoaming agent, catalyst and curing agent.

[0068] The mixer was preheated to 60?2? C. and the components of the precure added and heated for 15 minutes. The precure was then mixed for 30 minutes and the mixer blades and bowl scraped to ensure that any unmixed material was transferred to the mixing zone of the bowl. Defoaming agent was added and the composition mixed until the viscosity reducing effect of the defoaming agent is observed, this was measured as described in Example 5 and in this example required stirring for 25 minutes. The DBTL was added and the composition mixed for 15 minutes, then the IPDI added and the composition mixed for a further 15 minutes. The mixer blades and bowl were scraped to ensure that any unmixed material was transferred to the mixing zone of the bowl. After mixing the viscosity of the composition was recorded using a Brookfield viscometer (60? C.).

[0069] The composition was cast and any excess mixture removed from the shell housings. The charges were cured for 5 days at 65?2? C.

[0070] 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.