Experimental Determination And Mixing Mechanisms Research In The Novel Co-rotating Non-twin Screws

The self-cleaning co-rotating twin screw extruders are widely used in the polymer processing industry due to its excellent performance in mixing capability, self-cleaning and degassing efficient. However, the conventional twin-screw groups possess the symmetry between the two screw configurations, where fluids will found the similar geometrical space channel. It comes with the lack of transformation of different motion space and efficient mixing is presented owing to the little effect of the re-orientation of shear action. To achieve more efficient mixing, the symmetry breaking effect in terms of chaos dynamics is introduced, and the novel co-rotating non-twin screw extruder is invented. Moreover, the investigation is focused on such novel screw configurations in the paper. After the experimental machine with such non-twin screws is developed by us, the investigation of kinematics mechanism of mixing during extrusion is carried out using the numerical simulation combined with the experimental research of polymer filled with nano-CaCO3. It is no doubt of significance in science and reality.The new concept of the dissymmetry modeling for fully wiped co-rotating screws is presented in the paper. The physical and mathematical models are proposed, and then the fluid is assumed to obey the Carreau constitutive model. Using the mesh superposition technique provided by the finite element package Polyflow, the flows in the2D cross-sections, kneading Discs and screws elements are simulated respectively. The periodical distributions in velocities and pressure profiles are obtained. Adopting particle tracking technique, the mixing dynamics performances are characterized, The segregation scale is obtained by statistical methods. Mixing parameters such as mixing index, length stretches, instantaneous efficiency, and time-average efficiency are calculated. The local RTD for different screw groups are also investigated, and then the differences in mixing between different groups are detailed. The results confirm the fact that the novel co-rotating non-twin screw group is superior in the ability of mixing and more obvious chaotic mixing will occur in such novel geometries. In addition, the results of mixing evaluation parameters stated above from the2D simulation of simplified model find the similar trends compared with those from the three dimensional models for kneading Discs and screws elements.For the first time, the new extrusion system is designed and experimental machine is developed. The extrusion experiment is carried out on the novel co-rotating non-twin screws and the conventional co-rotating screws using the polymer such as LLDPE filled with nano-CaCO3with different weight ratios. The micro-structure of extrusion sample is characterized and analyzed by the SEM where the more efficient mixing is found prepared by the novel non-twin screws when compared with the conventional ones.The SEM results are in large agreement with the numerical simulation results. This shows the numerical simulation method is reliable and reasonable to some extent, and it comes to the conclusion that the novel co-rotating non-twin screw group is superior in the ability of mixing. So the further investigation will aim at the more details about the kinematics mixing performance occurring in such novel co-rotating non-twin screws, such as Poincare section, length stretches of interfaces, and so on.