Research On Coating Process Of Super-porous Propellant And Combustion Properties

In order to further improve burning progressivity and obtain better ballistic performance of propellant,a super-porous coated propellant with high burning progressivity was designed and a combustion mathematics model of the propellant was established in this paper.Due to big particles,complex surface structure,coating thickness of the propellant was more likely to have nonuniformity.The super-porous coated nitroguanidine（NGu）propellant with acceptable coating quality was prepared by drum coating method.Then the main process parameters were optimized by three-dimensional video microscopy（3DVM）and scanning electron microscopy（SEM）which were used to study the microstructure and thickness of the coating-layer.The optimal process parameters were also optimized by comprehensive evaluation index including the closed bomb test.Moreover,the stability of the coating material and its compatibility with the propellant were studied by differential scanning calorimetry（DSC）.Through a closed bomb test,the results have concluded,including the flame retardant law of propellant with different titanium dioxide（TiO₂）content coating materials;the burning performance of single-hole,19-hole,super-porous propellant;the combustion performance of super-porous coated propellant and its 1:1 mixed charged with the super porous propellant.The analysis of the burning surface showed that the splitting instant surface of the super-porous coated propellant increased by 3.32 times compared with the initial burning surface（eg.19-hole uncoated propellant:1.67 times,super-porous uncoated propellant:2.39times）.It was proved that the coating treatment technical was feasible to improve the burning progressivity.Compatibility between the coating material and the NGu propellant is level one and T_p0 of the mixed system is 186.08 ^oC.The aboved results demonstrated that it had good stability in general storage and use environment.The results of closed bomb test indicated that TiO₂ reduces the burning rate of the coating-layer,and the flame retarding effect increases with the increase of TiO₂ content.Compared with the 19-hole propellant,under normal temperature,low temperature and high temperature conditions the P_r value of the super-porous propellant increased by 24.1%,69.9%,and 28.5%,respectively,and the increase was greatly improved.Moreover,theΔL value of coated propellant（the mass fraction of coating-layer is 18%）increased by 369%,231%and197%under normal temperature,low temperature and high temperature conditions,indicating that the burning progressivity of the super-porous propellant was improved obviously after coating treatment.For the 1:1 mixed charge of the super-porous coated propellant with different coating-layer thicknesses,the t_m was found to be prolonged compared with the uncoated propellant.And the added time increased with the increase of the thickness of the coating-layer and the burning progressivity of coated propellant is optimal when the thickness of the coating-layer is 8%.It can be seen that the burning progressivity is not proportional to the thickness of coating-layer.It is necessary to select the appropriate coating-layer thickness according to the requirements of actual ballistic performance.