Fabrication And Performances Of Microcellular Combustible Cartridge Case Using Supercritical CO₂

Combustible cartridge cases are a kind of special propellants with special inner structure. They are made of combustible materials and can burn out completely along with main charge after firing, providing more projectile energy. To guarantee complete combustion, porous physical structure is required, so the manufacturing process is the key problem. In this paper, supercritical fluid foaming technology was used for making microcellular combustible cartridge cases and analyses of the relative performances of this kind of cases were also made. The main contents are listed below:Heat resistant explosives were chosen as energetic component. According to the comparison of properties and economy, RDX was chosen as energetic component in the experimental stage. According to the processability and foamability, polymethyl methacrylate and cellulose acetate were chosen as inert binders.The solvent method and supercritical fluid foaming process were designed and used to produce microcellular cartridge case. Extruding moulds and foaming moulds were designed and machined. The solvent ratio, moulding pressure and driving-solvent method were also studied. The method to produce microcellular cartridge case was determined by exploratory experiment. Finally, the properties of the basic formulations were tested, such as energy level and burning characteristics. The required RDX content was determined to guerantee complete combustion by closed bomb test.Weight method was used to analyses the sorption and diffusion behavior of supercritical fluid in combustible case, the influence of saturation temperature and pressure on the sorption and desorption process was studied. Nucleation and growth of micropores are studied and observed. The competitive relation of heterogeneous and homogeneous nucleation was also studied. The influencing factors on porous structure of cartridge case are analyzed. The influences of process conditions on porous structure in rapid depressurization method and two-step heating method were studied, and the results provided control method to obtain the desired inner morphology.TG was used to analyze the thermal decomposition process, and the results showed fractional decompostion for combustible cartridge case material. Vented bomb was used to study the surface morphology of combustible case with different burning degree, and the results showed that the burning behavior deviates from Vieille’s law and current predictions of interior ballistic simulations fail when based on a straightforward use of it. Then, closed bomb test was used to anlyses the influencing factors on burning characters in the foaming process.Constrained foaming process was designed and used to produce microcellular combustible cartridge case with good surface behavior and desired density or porosity. Relative foaming moulds were designed and fabricated. The influence of constrain foaming on porous morphology was studied and the influence of foaming conditions were also studied. The constrained foaming samples were tested in closed bomb to investigate burning behavior. Samples were tested under different ignition pressure, loading densities. Samples with different initial temperautures were also tested.The performances of microcellular combustible case, such as thermal stability, sensitivity, components compatibility, moisture absorption, heat resistance, and mechanical properties were tested, the methods to reinforce the case were also studied.