Simulation On Melt Segment In Vane Extruder

At present, the screw machinery is commonly adopted in the polymer processing industry,such as screw extruder, screw injection molding machine, etc. In the screw machinery, thepolymer plasticating and conveying process is mainly depending on the drag effect of therotating screw to the materials, which means friction drag in the solid materials conveyingprocess and viscosity drag in the melt conveying process, and the whole process is dominatedby the shear stress. Therefore, the screw plasitcating and conveying mechanism based on theshear rheology, usually exists some disadvantages, such as long thermo-mechanical history,high energy consumption, strong dependent on the characteristics of the materials, etc.However, the vane plasticating and conveying method and device based on extensionalrheology realizes the plasticating and conveying process is dominated by the normal stress，which has many advantages compared to the tradition screw extruder, such as higheradaptability to materials, shorter thermo-mechanical history, lower unit energy consumption,higher quality of the products, etc.It is helpful to thoroughly reveal the characteristics and laws of the flow field in theplasticating and conveying process in the vane extruder to do numerical simulation of theflow field in the periodical melt conveying process in the vane extruder. It is to study theeffects of the geometric parameters and rotating speed to the characteristics of the flow fieldin the vane plasticating and conveying unit.This paper utilized the viscoelastic fluid dynamics calculation software POLYFLOW tostudy the flow field in one vane plasticating and conveying unit in the melt conveying processof the vane extruder. The result showed that: It would generate the flow along the extrusiondirection because of the change of the cavity volume when the rotator was rotating in the vaneplasticating and conveying unit. The flow was the combination of drag flow and pressure flowaccording to the flow speed in the melt higher than that in the drag speed on the wall. Thepressure in the melt decreased along the extrusion direction. The instantaneous flow in theexit of the vane plasticating and conveying unit existed amplitude fluctuations. It used themixing index to characterize the degree of the extensional effect on the melt in the vaneplasticating and conveying unit. It existed the region in the vane extruder in which the mixingindex was over0.5, the highest value to0.95. It showed that the melts were suffered by theinteraction of the shear flow field and the tensile flow field. The extensional effect on the meltand the instantaneous flow rate or output in the vane platicating and conveying unit increased with the increase of the rotating speed of the rotator, the length of the vane, the inner diameterof the stator, the eccentricity of the rotator and the stator. However, the fluctuation range ofthe instantaneous flow rate increased when the eccentricity increased.