TECHNOLOGY AREA(S): Materials OBJECTIVE: Develop and demonstrate alternative methods for mixing of high-energy, solid propellants for large, up to 20 gallons in volume, gas generators for Navy strategic missile post-boost propulsion systems, other large missiles, and launch vehicles. DESCRIPTION: The current state of the art for producing high-energy, solid-propellant gas generators involves mixing energetic materials in a large bowl using impellers, i.e., rotating blades, until all the formulation ingredients are incorporated into one homogeneous mixture. Mix times are measured in hours, and during this time the rotating impellers are in direct contact with materials having a hazards classification of 1.1 explosives. Accidental fires have occurred when foreign object debris (FOD) have fallen into the mix bowl, and contact with the rotating blades caused a spark. The primary objective of this topic is to develop, demonstrate, and validate a new manufacturing process that does not include impellers for mixing large quantities of high-energy, solid propellants. Resonance acoustic mixing (RAM) technology is a new approach to processing in which low-frequency, high-intensity vibrations are used in place of impeller blades to generate the shear field required to mix high-energy, solid materials. Also, RAM technology eliminates the need for cleaning the impellers at the end of each production run. This advantage reduces the amount of generated hazardous waste containing explosive materials. Any new mixing technology must demonstrate that it can reliably produce a homogeneous mixture that yields a product with properties equal to that obtained using the legacy process. The design and analysis of the new processing method occurs first and is validated using mixtures of inert materials; at this step, validation is a comparison of the dispersion of ingredients as well as the mechanical properties of materials mixed with the new technology versus the legacy method. When acceptable results are obtained using inert materials, then the new mixing process is applied to high-energy, solid materials used for large gas generators. Validation using energetic materials is accomplished with a comparison of the physical, ballistic, and mechanical properties of the same gas generator propellant formulation mixed using the new technology versus the legacy method. PHASE I: Phase I includes a technology survey, evaluation, and trade studies to establish what both the current operational and developmental needs are for gas generator manufacturing mixing technology, especially those requirements related to safety, cost reduction, and environmental impact. The evaluation in Phase I relates to the possible candidate mixer technology that, for safety reasons, does not use blades. The process variations in mixing may include mix in case, mix in multiple batches, mix as a single batch, continuous mixing, or other techniques. Each variation is evaluated against the requirements. The small business may choose to demonstrate their technology using Inert propellant formulations. The inert formulation should be chosen to mimic energetic formulation mechanical properties. The deliverable of Phase I is a report that describes the down-select process to the most promising mixing method and results and conclusions from any inert propellant mixes that were performed. PHASE II: Design, analysis, fabrication, and test of the candidate mixer. Materials are purchased and assessed for quality. Inert mix trials are conducted to optimize process conditions. Naval Air Warfare Center (NAWC) China Lake will make subscale mixes of energetic propellant formulations using the down-selected approach. NAWC will perform physical, ballistic, and mechanical tests on the propellant and assess the results. The deliverable from Phase II is a report that describes progress on the design, analysis, fabrication, and test of the mixing hardware for the down-selected approach; also included are the results and conclusions from the subscale, energetic propellant mixes. PHASE III: The scope of Phase III includes a full-scale demonstration of the mixing technology using an energetic gas generator formulation at NAWC China Lake. The small business will be funded to provide the mixing equipment for use by NAWC China Lake, and the demonstration will be conducted by NAWC China Lake personnel. The mix process will be used to mix propellant ingredients at the 20-gallon scale. Propellant samples from the full-scale mix process will be tested for physical, ballistic, and mechanical properties. Results will be compared to those from the same formulation mixed using the legacy, rotating-blade method and an assessment of these results will be made as well as recommendations for future work. Following this demonstration, the technology could be transitioned to D5 gas generator production. The gas generator supplier may also use this technology for commercial and other government missions requiring gas generators (space launch, missile defense, orbital insertion). The deliverable from Phase III is a report that describes the full-scale test hardware and procedures; also included are results and conclusions from propellant samples made using the RAM method and the legacy method. REFERENCES: 1. Uniform Distribution of Minor Materials During Powder Mixing: https://www.researchgate.net/profile/Scott_Coguill/publication/270216427_RESONANTACOUSTIC_R_MIXING_UNIFORM_DISTRIBUTION_OF_MINOR_MATERIALS_DURING_POWDER_MIXING/links/54a2c3ec0cf267bdb90426ac.pdf?origin=publication_list2. Investigation of Acoustic Dryer for API Processing: https://www3.aiche.org/Proceedings/Abstract.aspx?PaperID=2293483. Processing and Formulation Challenges for Cost Effective Manufacturing: http://imemg.org/wp-content/uploads/2015/06/6B2-17235-ResonantAcoustic-Mixing-Processing-and-Formulation-Challenges.pdf4. Effect of Resonant Acoustic Mixing on Pharmaceutical Powder Blends and Tablets: http://fulltext.study/preview/pdf/143900.pdf5. Evaluation of Resonant Acoustic Mixing Performance http://fulltext.study/preview/pdf/235596.pdf KEYWORDS: Resonance Acoustic Mixing (RAM); Propellant Mixing; Gas Generator Manufacturing; Energetic Materials Processing
