Study On Sequential Solidification Process Of DNAN Based Melt Cast Explosives

Melt casting charge is a process of melting mixed explosives and injecting them into the body to cool and solidify.Due to its low cost and not limited by the shape of the interior of the body,it is widely used in conventional ammunition.As a new generation of low sensitivity fusion casting carrier explosives,DNAN can enhance the damage ability of ammunition by improving the solid phase high-energy components.However,during the solidification process of the slurry,there are physical phenomena such as phase transformation and crystallization,which can easily form defects such as pores,shrinkage holes,and cracks.Therefore,improving the charging process and reducing defects are research hotspots to improve the quality of the charge.In this paper,numerical simulation methods were used to study the modeling of sequential solidification process,the effect of process parameters on charge quality,and the relationship between process parameters and quality of high solid content DNAN based melt cast explosives.The main research contents are as follows:(1)Based on the analysis of the solidification process of melt cast explosives,a finite element simulation model was established to analyze the variation of the temperature field,the solid-liquid phase transition,and the mechanism of defect formation during the solidification process.An experimental scheme was designed for the measurement of the slurry temperature field using fiber Bragg grating sensors,which verified the rationality of the simulation modeling method.(2)Based on the principle of sequential solidification,a dynamic water injection sequential solidification process scheme was designed.The water injection process was modeled using the moving boundary method,which was more accurate than the traditional method of configuring jump curves.On this basis,simulation studies were conducted on the impact of typical process parameters such as initial slurry temperature,water temperature,and mold water injection speed on the charge quality.The results show that increasing the slurry temperature and preheating the mold are beneficial to reducing shrinkage defects;If the injection speed of the mold is too slow,the solidification time of the slurry increases,and the efficiency decreases;If the speed is too fast,the slurry cannot solidify layer by layer,and defects easily form in the axial region;The riser structure and heat preservation time have a certain impact on the defects of the grain mouth.(3)Based on the research on the influence of process parameters,a 4-factor and 3-level orthogonal test scheme was designed.Using shrinkage porosity and solidification time as evaluation indicators,the primary and secondary order of factors under different indicators was obtained using range analysis method;Considering the two evaluation indicators comprehensively,the optimal scheme under the optimal combination of process parameters was obtained using the gray correlation analysis method,which reduced the shortest solidification time by 5.7% compared to the orthogonal test,and decreased the minimum shrinkage porosity by 61.18%.(4)Based on the law of solid phase point migration and the principle of sequential solidification,a new variable speed water injection process was proposed.The simulation results show that the shrinkage porosity of the variable speed water injection process is reduced by 29.69% compared to the orthogonal optimization scheme,fully demonstrating that the variable speed water injection process can more effectively control the generation of defects.The above research results can provide a reference for the design of DNAN based melting and casting charging process.