Scale-Up Study Of Single-Screw Extruder For High Solids Propellant

Due to the continuous extrusion of single screw extruder production method is conducive to automation transformation,and the quality of the processed propellant products are uniform and stable,burning characteristics are excellent,it becomes a vital processing method for such special materials as high solids content propellant.With the ongoing development of China’s national defense and military forces,there are greater requirements for the delivery and surprise defense capabilities of rockets,missiles and other military equipment,which has higher requirements for propellants and products as the main source of power to deliver weapons.Under the current conditions of no breakthrough in propellant energy density,there is a need to increase the propellant yield and product size.The current single-screw extruder for highsolid propellant does not meet this requirement because of the limitation of screw size.So,it is necessary to develop the corresponding large-size equipment.This thesis is based on this need to design large-size extruders using the similar scale-up method based on an existing small single-screw extruder that operates safely and stably,as well as to establish a targeted scale-up model.On this basis,the field parameters of the extruder before and after the scale-up are simulated and compared by Polyflow and VEL simulation software respectively,while the scale-up model is revised according to the simulation results to guide the subsequent series design of this extruder.The main work completed in the thesis is as follows:(1)Based on the conveying characteristics of different functional sections of single-screw extruder,the dimensionless method is used to establish an exponential model for the scale-up of field parameters for single-screw extrusion with high solids content propellant which can be used as a basis for subsequent determination of the scale-up index of screw parameters,and also to predict the relevant field parameters of the target extruder during the design of subsequent extruder series;(2)Taking into account the experience of designing single-screw extruders in the field of polymer processing,while ensuring that the average shear rate and area/output ratio remain the same before and after scale-up.The scale-up indices for barrel/screw clearance,screw width,screw clearance,and screw length are determined to be 1,while the scale-up index for screw speed is-0.5and for screw depth is 0.5.Two groups of target extruders,φ90 and φ120,are designed and simulated according to the preliminary determined screw parameter indices,and the results show that the output of the two target extruders increased by 3.36 times and 6.37 times.The distribution of solid bed and pressure distribution along the axial direction are basically identical to those of the reference extruder.The highest shear rate and average shear rate are lower than those of the reference extruder,while the temperature distribution are higher than those of the reference extruder;(3)The initial derivation of the scale-up index equation for some field parameters is inaccurate,and its predicted value deviate from the simulation.The influence of the screw parameters on the field parameters is investigated by orthogonal tests,and the single-factor variable method is used to simulate the screw parameters with significant influence to obtain the influence trend,and the scale-up index equation is corrected by combining the significance judgment results and the influence trend;(4)According to the modified field parameter scale-up index equation,the new screw parameter scale-up index is determined and two new target extruders are designed.Comparing the simulation results of the extruder before and after the scale-up,the plasticization characteristics and along-stream pressure distribution of two target extruders are similar to those of the reference extruder,but the average and maximum along-stream temperatures are still higher than those of the reference extruder.By adjusting the process temperature,it can be seen that lowering the barrel and screw temperatures can reduce the alongstream temperature,but at the same temperature reduction rate,lowering the barrel temperature is more effective in controlling the highest along-stream temperature,while lowering the screw temperature can effectively control the average along-stream temperature.