Performance Analysis And Experimental Study On Screw Element Of Twin-screw Kneader

Twin-screw kneader, one kind of polymer processing equipment, has good performance such as conveying, mixing, plasticizing, shearing effect and is widely used in rubber industry, medicine and food industries. The core components of twin-screw kneader are two screw rotors, and shear ability, stretching performance, mixed ability of the screw rotors is directly affected by the design of end cross-section profiles, so researches on the design of end cross-section profiles and performance of screw rotors play an important role in the development of new screw elements and improving of the performance of screw rotors.In this article, based on the forming mechanism of the end cross-section profiles of screw rotors, three groups of end cross-section profiles are chose as the research object, and flow field analysis and mixing performance comparison of the corresponding three groups of screw rotors are implemented, then influence of design parameter and process parameter on mixing performance of the twin-screw kneader is discussed, finally, the visualization study of mixing process is done by one novel twin-screw kneader. The research results have provided basis to choose screw rotors with excellent performance and the appropriate screw parameters, meanwhile the guidance to the visualization study of mixing process. The main work of the research is as follows:(1) After demonstrating the study background and significance in this article, the current development situation of domestic and foreign twin-screw kneader and screw elements is analyzed, and the research progress of performance and profiles of twin-screw kneader is described;(2) Two kinds of methods to form the screw rotor profiles are introduced, which are the relative motion method and the meshing principle method, respectively, then the design of rotor profiles based on the idea of functional method is discussed to explore the new way for the design of end cross-section profiles. The unified expression form of specific curves segment on the profiles of conventional and differential screw rotor is given and the main research object is established;(3) Simulation of flow field and mixing performance analysis are implemented for the three groups of screw rotors, and the control equations of transient simulation process, the evaluation parameters and the statistical parameters are given, flow field analysis is carried out by extracting the parameters such as velocity, pressure within the given lines and surfaces, and the performance of different screw configurations are compared based on the statistical knowledge combined with the particle tracing method using residence time, segregation scale, the time average efficiency, maximum shear/stretching rate and other parameters;(4) Tip angle which is the important design parameter of screw rotor profiles directly determines the size of the screw edge and screw groove, five groups of tip angles are selected to study the evolution process of screw rotor profiles and the influence of tip angle on the mixing ability which is verified by experiment. Tip clearance, as the important process parameter of twin-screw kneader, affects the mixing process of material particles and the proportion of particles subjected to high shear and stretching effect, and four groups of tip clearances are selected to study the effect of tip clearance on the mixing ability of twin-screw kneader.(5) Visualization research on the mixing process is implemented by building one novel twin-screw kneader experimental platform combined with the limited experimental conditions, and it provides guidance for the research of twin-screw kneader’s mixing process.