Numerical Simulation Research Of Rheological Behavior For The Screw Extrusion Molding Process Of Double-base Propellant

Extrusion process is an important production process of double-base solid rocket propellant. It mainly includes single-screw and twin-screw production process, in which the single-screw extrusion process accounts for a large proportion. In the actual production process, it needs to provide high screw temperature for easily extrusion. In addition, because of strong extrusion force, the energetic materials in the solid propellant could burn and explode easily. So there were many accidents in the production of solid propellant. However, because of the complexity of the flow characteristic in screw extruder, it was difficult to study the influence of rotational speed, temperature and other parameters on the safety of extrusion process by experiments. In addition, it may lead to accidents when we change the normal conditions. With the continuous development of numerical simulation techniques, it will be viable to solve this problem by simulation technology. In this paper, according to the transient model, the POLYFLOW software was used to study the screw extrusion process of GR-35 double-base propellant. We wanted to find an appropriate simulation tools and methods to simulate the extrusion molding process of the energetic materials.Firstly, the Gambit software was used to establish and mesh for screw model and die model. Then overlapping mesh method was used to mesh generation for screw model to ensure the accuracy of the calculation. Moreover, according some material parameters and extrusion process of GR-35 extrusion process and power rate equation, the boundary conditions of extrusion process and molding process were obtained by nonlinear fitting process. Then according to the transient model, the changes of some parameters under normal process conditions during extrusion can be obtained, such as temperature of propellant, pressure, shearing rate, velocity and so on. According to the simulation results, the temperature, pressure, shearing rate and velocity all become larger in screw arris position. In addition, the values of temperature, pressure will increase while the velocity and the shearing rate will decrease as the extrusion processes. The results show that he physical parameters are constantly changing in the propellant extrusion process. If the screw is longer, the temperature will change more obvious, which means more dangerous.In this paper, the effects of different parameters on the material parameters in screw extrusion process were studied, including screw speed, screw temperature and the temperature of the sleeve. The results showed that, in the same position of the screw, with the increasing speed, temperature of materials, pressure, shearing rate and velocity are increased. Furthermore, with the screw temperature or the temperature of the sleeve increased, the temperature of materials and velocity were increased, while pressure and shear rate decreased. The influence of screw temperature is more obvious than that of the sleeve temperatures. Therefore, the external temperature changes may significantly affect the parameters of materials. So in the actual production process, the temperature will be hold in the controllable range. Otherwise, it will be easily lead to bight-variability of material temperature and pressure parameters, and may even cause combustion and explosion hazard.For extrusion die, the Gambit software was used to establish the die model and mesh generation, and refinement the grid on the surface of model. Then the material parameters under normal conditions of GR-35 molding process were obtained. It can be found that, the material temperature, shear rate and velocity changed significantly from the entrance to the exit, and become stability after the GR-35 entering the molding section. while the pressure will changed significantly after the GR-35 entering the molding section. When the length of molding section changed, material temperature, shear rate and velocity has no significant change, while the pressure changed obviously. In addition, the longer the molding section means the greater the extrusion pressure.