Study On The Screw Design Of Melt Conveying Section In Co-Rotating Twin Screw Extruder

The co-rotating twin screw extruder plays an important role in the industrial compounding and processing of polymers, and its structures of modular screw and barrel can provide good adaptability and mixing to different blending tasks. Melt conveying is one important processing of the extrusion processing (which usually contains solid conveying, melting, venting and melt conveying.), its conveying character and mixing ability directly influence the extruder’s production. In this paper, with numerical simulation and experiment, the screw design methods of melt conveying section in co-rotating twin screw extruder was studied.Two methods of screw element’s3D modeling were generalized:one is based on the curve of screw’s cross section; the other is based on the curve of screw’s axial channel.An extruder design method of "large screw simulation-similar scale up-experimental screw simulation-experiment" was presented. The scale up methods was:screw and barrel configuration was according to geometry similarity, volume scale up determined output, average shear similarity defined screw speed. And the average shear rate was calculated by simulation, a ratio of volume conveying was used to calculate the screw diameter and other parameters. The theoretical max ratio of volume conveying was used to evaluate the screw element’s positive-displacement pumping, and the theoretical max ratio of volume conveying can be calculated from simulation the curve of△P-Q. The ratio of volume conveying should be the range of10%～20%in a screw design.The pressure build and full filled length was studied, and the results were followed:the screw element unit’s pressure build approximately equal to the sum of every single screw element’s pressure build, the full filled length can be detected by the pressure build. Then, with this, the screw element’s type selection and length design can be optimized.The SME (screw mixing element) element’s mixing character and its configuration optimization was simulated and experimented. The results show that:the SME is a good distributive mixing element; the distributive mixing of screw configuration (in which the SME located at its top) is strongest.The screw’s axial force and torque were simulated and verified by experiment. Experimental results show that:the screw’s axial force is composed by static pressure force of die and additive force along the screw.