Simulation Research On The Single-screw Extrusion Process Of Energetic Materials

Energetic materials are indispensable materials for the national defense industry and aerospace technology.And research on their processing methods has always been a hot spot in many countries.The screw extrusion molding process is an important method for the processing of energetic materials,including several processes such as material mixing,water removal,calendering plasticization,granulation and screw extrusion.With the in-depth study of energetic materials,high-energy energetic materials have been developed rapidly,and the structure and process of using traditional extruder cannot meet the higher requirements for the development of energetic materials.In this context,it has important theoretical significance and industrial application value for carrying out simulation research on the screw extrusion processing of energetic materials,using relevant theory to guide the design of the screw extruder and controlling the key parameters such as forming pressure,temperature and shearing of material to achieve the continuous and stable production of the columnar products.In this thesis,the physical model and mathematical model for the full groove single screw extrusion process of energetic materials were established firstly,basing on the theory of grooved single screw extrusion plastic molding.Based on the material properties of the modified double-base propellant,Virtual Extrusion Laboratory software(VEL)was used for the first time to simulate the entire screw working section and mold of the single-screw extrusion process to obtain changes of various parameters along the extrusion direction,which help to provide a reference for the safe extrusion process.Then the POLYFLOW software was used to simulate and analyze the homogenized section of the screw and the mold section.And the results of VEL were verified and further supplemented in terms of the overall distribution trend and specific values.The main research work is as follows:(1)A three-stage theoretical model of the whole straight groove single screw extrusion process of energetic material was established.It was determined that the boundary condition of positive displacement conveying is that the solid plug is not destroyed by shear force in the solid conveying section,which will provide theoretical support for the design and optimization of the barrel and screw.(2)POLYFLOW and the extruder module of VEL were used to analyze the whole screw working section of the single-screw extrusion process of the modified double-base propellant.The results showed that the peak pressure appeared on the front side of the screw arris at the end of the compression section.The temperature in the middle of the channel on the backside of the screw arris is the largest,mainly caused by shear heat generation.Therefore,it is necessary to pay attention to the shearing to avoid overheating during the extrusion process.(3)The influence of processing technology and screw structure on the screw extrusion process was studied by using VEL software.The results showed that screw temperature,screw speed and compression ratio of the screw had a greater influence on the safety extrusion process.The material temperature increased with the increase of screw temperature,while the pressure decreased.Increasing the rotation speed of the screw will cause a large temperature rise,which is likely to cause danger.So it is not appropriate to increase the rotation speed of the screw.The compression ratio of screw can be appropriately increased within the safe pressure range since it is beneficial to the pressure building process and does not cause too much temperature rise for increasing the compression ratio.(4)The 3D-FEM module and POLYFLOW were used to simulate and analyze the mold forming flow path for cylindrical products of the modified double-base propellant.It was found that the forming pressure decreased gradually from the entrance of the mold and the temperature rise caused by shear heating was small.And 3D-FEM module was used to study the influence of the temperature and shrinkage angle of mold on the mold forming process.The simulation results showed that the increase of the temperature and shrinkage angle of mold will reduce the pressure,which is not conducive to the compaction and bonding of materials.Therefore,the mold temperature should be as low as possible,and the shrinkage angle of mold should not be too large.