Polymer reactive processing is usually under the conditions of high temperature, high pressure and high shear. It is very difficult to study the micro physical quantities such as strain, stress and pressure, as well as the process statistics such as residence time distribution, maximum tensile rate and the percentage of each parameter stage. The experimental method can only measure the data of macro properties such as conveying capacity, conveying performance and medium rheological performance per unit time: the kneading and extrusion characteristics of some simple screw profiles and single materials can be analyzed by analytical method, but most conventional screws have complex shapes, which makes the material flow in a three-dimensional state, and it is almost impossible to solve them by analytical method. At present, numerical calculation method is widely used. Computer simulation technology is used to analyze the reaction mechanism of polymer processing, observe the local micro rheological behavior of flow field, and realize the quality prediction and control of twin-screw kneader in the design stage.
Shon and other scholars studied the mixing state of polypropylene and polyamide in the ratio of 3:1 in several kneaders that can work continuously, such as combined meshing co rotating twin-screw kneader, counter rotating twin-screw kneader, BS kneader and tex-t Kobelco mixer. The results show that the co rotating twin-screw element has the best distributed mixing performance, and the non rotating twin-screw element has greater axial conveying capacity. Based on the convective Maxwell model, Yu et al of Sanyo research center in Korea used numerical methods to simulate the thermal coupling effect of nonlinear viscoelastic fluid in buss kneader when the screw rotor is rotating and oscillating at the same time. It is found that the pumping capacity of threaded elements changes with the change of material viscosity and kneading time. Japanese scholars%. The flow pattern and mixing mechanism of materials in co rotating twin-screw kneader were analyzed by analytical method.
Lombois burger et al. 22 analyzed the kneading and extrusion characteristics of polymers by numerical methods. Bakalis et al. Studied the material flow characteristics in the meshing area of co-directional self-cleaning twin-screw kneader. Kumar and other scholars constructed the time distribution model of high viscosity fluid in twin-screw kneader under ideal state. Eitzlmayr and other scholars used the smoothed particle hydrodynamics (SP) method to study the hydrodynamics and mixing characteristics of the co rotating twin-screw kneader respectively. Fard and other scholars used the surface mapping method combined with the velocity field calculated by the finite element method to analyze the dispersion performance of the threaded element and the mixing element respectively.
Domestic scholars have also studied the screw elements of co rotating twin-screw in various aspects. Hu Dongdong and others used polyflon to statistically analyze the polymer mixing state in the same direction and different direction screw kneader respectively. The results show that the same direction twin-screw kneader is better than the different direction twin-screw kneader in mixing performance. Zhang Xianming summarized the research progress of time residence distribution, studied the extrusion residence time distribution through analytical method, experimental method and numerical calculation method, and obtained the parameters characterizing the mixing characteristics by numerical calculation method. Compared with the experimental results, the results show that the numerical simulation method has high accuracy. Long Zhibin et al. Used poly1ow to numerically simulate the twin-screw hump element, and compared the performance of the hump element with that of the conventional double head thread element from the perspectives of element pressure building capacity, shear capacity and axial reflux. It is proved that the hump element has good pressure building capacity and axial mixing capacity, and has weak shear effect, It is suitable for high-speed extrusion and mixing of heat sensitivity and shear sensitivity such as biodegradation. Shi baohu et al. Described in detail the structure of new components in co rotating twin-screw kneader and compared their performance. Peng Tao and Huang Fengchun studied the mixing effect of different threaded elements. Yu Huiwen and others designed the end face profile of differential co rotating twin screw according to the principle of relative motion, studied the influence of asymmetric co rotating twin screw end face on mixing behavior, and pointed out the existence of chaos in the mixing of co rotating differential screw rotor. Based on boy's screw meshing theory and from the perspective of screw assembly and processing, Bi Chao and others analyzed the mechanical properties and mixed performance parameters such as bearing force of the screw to the bearing box, screw torsional deformation, specific energy consumption, stop time distribution and so on modified by the normal equal clearance correction method and the center distance correction method by using ANSYS and polyflon finite element software respectively, It is concluded that the screw element obtained by the center distance correction method is slightly better in mechanical properties, but not as good as the screw element obtained by the normal equal clearance correction in terms of specific output and specific energy consumption.
