Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
2001-10-18
2004-05-18
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019900, C149S092000
Reexamination Certificate
active
06736913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improved processing of energetic materials, in particular explosives, such as those used in warhead, munitions, and other highly energetic applications. More particularly, the method of this invention allows for the processing of explosives containing high solid loads of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0.
5,9
0
3,11
]-dodecane (also known and referred to herein as “CL-20” and “HNIW”).
2. Description of Related Art
For most existing weapons systems, one of the most critical ingredients, if not the most critical ingredient, in terms of explosive performance is the energetic filler. CL-20, with its substantial increase in performance output, is an organic oxidizing compound presenting significant opportunities in terms of energy capabilities for explosives. For example, the use of CL-20 as part of the explosive charge in weapons systems may provide, in comparison to conventional energetic fillers, increased antiarmor penetration and enhanced missile/torpedo effectiveness and lethality.
Many cast explosives are manufactured entirely in batch processes. A discussion of conventional batch processes for processing cast energetic materials is set forth in the background section of U.S. Patent No. 5,565,150. Generally, in a batch process, mixing is performed by first introducing liquid ingredients into an appropriate mixer, such as a standard vertical sigma-blade mixer, to form a plasticized binder. Examples of suitable liquid ingredients include polymeric binders, such as hydroxy-terminated polybutadiene, and plasticizers. Among the conventional plasticizers most commonly used with hydroxy-terminated polybutadiene are dioctyladipate (DOA) and isodecyl pelargonate (IDP). After the liquid ingredients have been mixed thoroughly, the solid ingredients are added in a multistep fashion, with an equal proportion typically being added in each step. Because of the high performance expected of modem explosive devices, cast explosive compositions typically contain high solid contents on the order of about 85 wt % to 92 wt %. Examples of solid ingredients include the following: organic energetic fillers such as RDX (1,3,5-trinitro-1,3,5-triaza-cyclohexane), HMX (1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane); inorganic oxidizers, such as ammonium nitrate, ammonium dinitramide, and ammonium perchlorate; and metal fuels, such as aluminum powder. Once the solid ingredients have been blended into the plasticized binder to achieve homogeneity, a curative (e.g., a diisocyanate) and a cure catalyst (e.g., triphenyl bismuth) are added to cure the plasticized binder. Prior to full cure, the mixture is cast, for example, into the case of a warhead or suitable mold.
When an effective amount of plasticizer is used in combination with RDX or HMX as the energetic filler, the solid ingredients are wetted and coated and the mixture takes on a sufficiently low viscosity to create a relatively free-flowing suspension that is castable without too much difficulty. Generally, it is possible to employ an effective amount of plasticizer to establish a free-flowing suspension without causing the plasticizer to exude from the cast explosive.
However, the inventor has found that the conventional plasticizers used for batch mixing do not create a free-flowing suspension when mixed with high solid loads of CL-20. Although CL-20 shares an association with RDX and HMX inasmuch as each of these compounds is categorized as a nitramine, in the context of this conventional processing technique, CL-20 does not share the same synergistic compatibility with conventional plasticizers as RDX or HMX. The addition of high proportions of CL-20 to conventional plasticized binders, such as hydroxy-terminated polybutadiene plasticized in DOA or IDP, produces a high viscosity formulation having poor flowability. As a consequence, expensive processing equipment and high power expenditures are required for stirring large batches of castable explosive compositions containing high CL-20 loads to create the shear forces needed to homogenize the composition. Even with high shear mixing equipment, it is often only possible to attain marginal homogeneity in the cast material. It is also difficult to cast the high viscosity explosive without generating air pockets in the cast explosive. The presence of air pockets in cast explosives is highly undesirable, since air pockets increase impact sensitivity and decrease performance. Attempts to lower the viscosity of the mixture and attain homogeneity in mixing by the addition of high proportions of plasticizer have also been unsuccessful. The amount of plasticizer needed to homogeneously disperse CL-20 loads in conventional plasticized binders and create a free-flowing casting mixture is typically so great that the plasticizer exudes from the cast explosive material. The exuding of plasticizer from the cast explosive material can cause the material to shrink and separate from its surrounding case.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to fulfill a long-standing need in the art by providing a technique in which an explosive composition characterized by a high solid content, including a high proportion of CL-20 as one of the solid ingredients, can be processed without encountering the above-discussed problems of high viscosity, poor castability, and plasticizer exudation.
In accordance with the principles of this invention, the above and other objects are attained by a method of processing explosives in which at least one plasticizer selected from the group consisting of naphthenic oil and paraffinic oil is mixed with at least one binder that is miscible with the naphthenic/paraffinic oil. The plasticized binder is then combined with solid energetic ingredients, in particular CL-20, and optionally other solid ingredients, such as other energetic fillers, metal fuels, oxidizers, and fillers. The solid ingredients content of the explosive composition is preferably high, meaning that the total amount of polymeric binder and processing oil remaining in the cast explosive material is not more than about 15% by weight. Preferably, the solid ingredients content of the explosive material is in the range of about 85 wt % to about 92 wt %, more preferably 86 wt % to 91 wt %. As referred to herein, solid ingredients means ingredients that are in a solid state at room temperature, and exclude the polymeric binder and the plasticizing processing oils.
Unlike conventional plasticizers, when CL-20 is mixed in a binder plasticized with a sufficient amount of processing oils, the resulting explosive composition has a sufficiently low viscosity to allow for homogeneous mixing of the solid ingredients in the plasticized binder and to establish, prior to curing of the composition, a relatively free-flowing suspension that can be cast into a desired configuration without the formation of air pockets.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which explain the principles of this invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PREFERRED METHODS
The method of the present invention produces cast explosives without the need to rely on solvents and high-shear mixing equipment. Instead, the introduction of an effective amount of naphthenic oil and/or paraffinic oil as a plasticizer in accordance with the practice of this invention permits explosive compositions containing high solid ingredients contents to be processed at sufficiently low viscosities to establish free-flowing suspensions.
In accordance with this method, a binder system is prepared by introducing at least one liquid binder and at least one plasticizer comprising naphthenic oil and/or paraffinic oil into a mixer and intimately mixing the binder and plasticizer with each other to form a homogeneous miscible solution. As the filler is added, the viscosity of the mixture increases. Preferab
Alliant Techsystems Inc.
Miller Edward A.
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