DEVELOPMENT OF A HEAVY DUTY CO-AXIALLY PRESSURIZED CASTING MACHINE FOR HIGHLY VISCOUS NANO-ALUMINIZED PROPELLANT SLURRIES

Nano-aluminum powder can potentially increase the specific impulse of solid propellants in com-parison to those with micro-aluminum powders. However, this method of enhancement suffers from the challenge of producing high-viscosity propellant. No casting technique to date, whether the conventional vacuum or pressure casting, has been capable of processing nano-aluminized propellants effectively. Assessing the limitations of the traditional approaches of casting, we have developed a novel pressure casting equipment. This equipment can be used for casting propellants having vis-cosities up to 10 × 103 Pa s. A two-step pressurization technique has been evolved wherein the equipment pressurizes a low-viscosity dummy slurry, which in-turn pressurizes the high-viscosity, live, nano-aluminized propellant. A very effective pressurization and flow of propellant could be ob-tained. Nano-aluminized propellant having viscosity in the range of 4 × 103 to 8 × 103 Pa s was cast into a ballistic evaluation motor having a 3 kg propellant mass. The propellant grain was ho-mogeneous and defect-free. The formulation had nano-aluminum and mono-modal ammonium per-chlorate content of 17 and 68%, respectively. The ballistic data of this nano-aluminum propellant, having 84.5% active aluminum content, was compared to that of a conventional hydroxy termi-nated poly-butadiene–based micro-aluminum propellant, having active aluminum content of 99%. Even with the fall of purity by > 14%, the nano-aluminum propellant showed some rise in specific impulse by 5 N s/kg and characteristic velocity by 11 m/s. It is obvious that, with a higher level of purity of nano-aluminum, the specific impulse and characteristic velocity would improve by far. The increase in ballistic performance is on account of enhancement of combustion efficiency and the lowering of two-phase flow loss.