Study On Friction Safety Of Co-rotating Twin Screws For Solid Propellants

With the increasing energy and demand of solid rocket propellant,how to produce solid propellant more efficiently and safely will become the mainstream of research at home and abroad all over the world.Because of small dosage in barrel,high production efficiency and uninterrupted production,co-rotating twin screw continuous mixing process has become one of the most important directions for mixing propellants.But friction is unavoidable,the propellants are high energy and sensitive,as well as pressure,temperature and viscous shear stress are difficult to measure,how to mix solid propellants safely and stably still needs further study.In order to investigate the friction safety performance of solid propellant in the co-rotating twin-screw extruder,the following work is carried out on this subject:(1)Based on friction pendulum test,the finite element model of solid propellant tablet and metal spool is established.According to numerical calculation method,the distributions of temperature and frictional work are calculated to compare the changing regulations with different pressures and velocities.And friction power is put forward to evaluate the degree of friction.on the basis of the friction pendulum test,the ignition probability of the solid propellant under the above process is obtained.It is found that the frictional heat generation power and ignition probability have the same order when they are sorted separately.The results show that the friction heat generation power is suitable as an index to evaluate the severity of friction.Furthermore,the concept of critical friction power is proposed,lower than which the tablet will not ignite because of friction.(2)To compare and analyze the changes with friction-related parameters in the flow field of SE and KB screw elements,maximum shear stress and dissipated power are distributed in the meshing zone.This indicates that the friction inside the propellant slurry is the most intense here and simultaneously it is the most likely area of the entire flow field to be ignited or exploded by friction.(3)Based on the current twin-screw mixing section configuration commonly used for solid propellants,the maximum dissipated power of the flow field under different feed rates and different rotational speeds was calculated,and in the meantime,the feed volume,rotation speed and dissipation were analyzed.Combined with the critical frictional heat generation power,the critical dissipation power of the twin-screw flow field is determined,and on the basis of that,a reference is given for the preset of the process parameters in the twin-screw mixing process.