1. Field
This invention relates to a method to charge a container with energetic ingredients to produce solid propellants, explosives, or other energetic compositions. More particularly the energetic mixing is by non-contact means by achieving resonance of the ingredient slurry in batches, in near net shape containers, or in end-use containers such as rocket motor cases, warheads, or explosive liners.
2. Description of the Related Art
The preparation and loading of a propellant for a rocket motor or missile is a complex process requiring many steps and a significant amount of time. One conventional process includes the following steps: (a) preparing a submixture that includes a prepolymer, plasticizers and stabilizers; (b) forming a premixture by adding a fine aluminum powder to the submixture; (c) transferring the premixture to a mix bowl; (d) initiating batch mix by sequentially adding an oxidizer, such as ammonium perchlorate; (e) interim mixing under a vacuum to degas propellant slurry; (f) adding propellant curatives and catalyst; (g) final mixing and vacuum degassing propellant slurry; (h) transporting batch mix to casting area; (i) establishing cast tooling, conducting propellant transfer and casting propellant in motor case(s); (j) transporting cast motors to cure facility; (k) curing motors at elevated temperature, typically about 65° C.±15° C. for an extended period of time, typically from 4 to 21 days; (l) removing cured motors for post-processing and delivery to customer; and (m) decontaminating mix and cast equipment, and certifying for reuse.
The combined time for the three mixing steps, (d) batch mix, (e) interim mix, and (g) final mix, is on the order of 36±6 hours, especially for batches containing state of the art amine-type bonding agents. The period of time is dependent on various interim chemical reactions that proceed to achieve the final required or optimum cure properties in finished product. The extended period of time required for mixing and curing, as well as the time and expense for decontamination and recertification of tooling for reuse, make the conventional process time consuming and expensive.
A low frequency, high acceleration vibratory mixer is disclosed in U.S. Pat. No. 7,188,993 to Howe et al. The frequency can be adjusted to produce standing acoustic waves and resonant mixing greatly agitating fluids and/or solids leading to enhanced mixing at reduced times when compared to conventional mixing techniques. Further, the mixing does not require a rotating impeller to contact the mixture. U.S. Pat. No. 7,188,993 is incorporated herein by reference in its entirety.
An acoustic wave generating mixer of the type disclosed in U.S. Pat. No. 7,188,993 is disclosed in an MDA Update, summer 2004, and is used to blend metallized powders, gallants and liquids into a finished gel propellant, which is typically prepared by addition of gallants and metal powders to liquid fuels, or, alternatively, by addition of liquid oxidizers to particulate gallants, followed by final vacuum mix, and transfer to storage tanks. Although the mixing of metallized fuel gels or particulate-gelled oxidizers is facilitated, no cure chemistry is accommodated, nor is cured solid propellant or explosive fill castable compositions as a result.
Accordingly, there is provided a method to charge a container with an energetic mix. This method includes the following steps: (a) adding a plurality of particulate energetic mix constituents and a binder to the container; and (b) mixing the plurality of energetic mix constituents utilizing a non-contact mixer to form a homogeneous mixture within the container, and curing the binder to solidify the homogeneous mixture and bind the homogeneous mixture to the container.
The container may be a liner or pre-form intended for insertion into a device, or may form a portion of the device itself, such as an aft portion of a rocket motor or casing for an explosive device. Because the resonant mixer does not have a moving impeller or other component that contacts the energetic mix and the container is not reused, there is minimal decontamination required between each mix and the manufacturer may rapidly commence assembling the next device, rather than clean-up and recertification.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicated like elements.
With reference to
Each addition may be a dry particulate or a liquid, as one component or blends of two or more solid or liquid ingredients, varied to provide optimum mix of specific formulations for each purpose, either as propellant or explosive compositions. Components may be premixed or added non-sequentially to enhance manufacturability throughput, reduce hazards, or reduce cost by pre-processing by separate automated techniques in other optimized facilities.
In an exemplary energetic mix for use as a (castable) composite aluminized propellant; First 14, liquid or solid prepolymer, liquid plasticizer, liquid and/or solid stabilizers, aluminum powder, liquid bonding agents, possibly preblended as nonenergetic materials in appropriate low-cost facilities, approximately 30 weight percent; second 16, particulate or encapsulated oxidizer particles having a variety of size distributions to achieve specific ballistic performance, approximately 69 weight percent; and third 18, liquid curatives and liquid or solid cure catalysts or cure modifiers, approximately 1 weight percent.
With reference to
A vibratory mixer 24 contains a plurality of oscillator drives (not shown) that transfer vibration and acceleration to the container 12 by way of variable resilient members 26, such as springs at a frequency and amplitude effective to cause resonance. By way of example, the exemplary composition described above is effectively transformed to a substantially homogenous mix 28 by resonant mixing for a time of from 30 to 60 minutes at a frequency between 40 and 70 cycles per second and a linear motion between 20 and 60 grams per cycle.
Referring now to
The container 12 may be a liner or preform that is then inserted into a desired product, such as a housing of a rocket motor, or other projectile for artillery use, or an explosive device for shape charge applications. Alternatively, as illustrated in
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, elastic cases or containers having predesigned flexibility or elasticity may be selectively used in whole or in sections to allow variations in the mix resonance, establishing flow patterns that can be tailored, especially when used together with rod-like or fibrous ingredients, to build burning rate control of the end product during the mix process via selective orientation of the mix ingredients due to resonant mix patterns. Accordingly, other embodiments are within the scope of the following claims.
This application claims the benefit of U.S. Provisional Application No. 60/983,621, filed Oct. 30, 2007, which is incorporated by reference as if disclosed herein in its entirety.
Number | Date | Country | |
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60983621 | Oct 2007 | US |