Study on the mixing performance of a co-rotating conical twin-screw extruder

In order to provide theoretical basis and technical support for the design and actual processing of a co-rotating conical twin-screw,a study was done on the mixing performance of a co-rotating conical twin-screw extruder.The flow of rigid polyvinyl chloride(RPVC) was melted in a co-rotating conical twin-screw extruder.When the rotation speed was 25 r/min,the pressure difference between the entrance and exit of the extruder was zero,a co-rotating conical twin-screw extruder,a counter-rotating conical twin-screw extruder and a parallel twin-screw extruder were simulated by using Polyflow-the finite element method software.The three-dimensional isothermal flow fields of RPVC in the melting sections of the three types of twin-screw extruders were also calculated.The mixing performance of each type of twin-screw extruder was studied by using the particle tracking analysis method.The results of particle tracking analysis show that a co-rotating conical twin-screw extruder has the best dispersive mixing performance.Its distribution mixing performance is better than that of a counter-rotating conical twin-screw extruder and smaller than that of a parallel twin-screw extruder.The results show that a co-rotating conical twin-screw extruder not only has the advantage of compressing materials,but also overcomes the shortcoming of a lower shear rate compared with a counter-rotating conical twin-screw extruder.The fluctuation of pressure in the melting section of a co-rotating conical twin-screw extruder is the smallest,which allows for superior stability of the polymer extrusion in the three types of twin-screw extruders.The residence time of RPVC in an HT-30 combined parallel twin-screw extruder was studied through experiments and numerical simulation.The difference in results between the two methods was very small.Therefore,the mathematical and physical models as well as the numerical method in this study are reliable.