Design Theories Of Rotor Profiles And Its High-Performance And High-Precision Machining Method For Differential Twin-Screw Kneaders

It is difficult to study the twin-screw extrusion because of the complexity of geometry and the conveying performance of screw rotors. Differential twin-screw kneader is one kind of novel twin-screw mixing extruder which can be used for high viscosity material conveying, mixing and malaxating, kneading, voltage buildup and self-cleaning functions as well as can generate high shear stress for high viscosity material. The key parts of the differential twin-screw kneader are one couple of intermeshing screw rotors. And how to design and machine the screw rotors is the key problem to enhance the performance of whole machine. This dissertation investigates the theories and applications on the profiles design, optimization and simulations as well as high-performance and high-precision machining of screw rotors from analyzing the key technology for the differential twin-screw kneader.The theories of profiles designing and mathematical model for the differential twin-screw kneader are established using theory of gear engagement as well as design method of twin-screw pump. The geometry and meshing properties of the differential twin-screw kneader are studied. The optimization model is built using optimum design method. The design parameters of female and male screw rotors are analyzed and the variable proportions of volumetric efficiency Cn are studied with distance A and tooth number ratio Imf changed. The equation of optimal distance A is deduced when the shivering and crumbing performance are considered. The equations of the profile curves of the female and male screw rotors as well as practical examples are put forward.The research is performed for the non-Newtonian fluid transported by the differential twin-screw kneader based on Finite element analysis (FEA) software. The performance simulations, velocity field and pressure field of the fluid, are analyzed. The static load of twin-screw kneader is introduced and a mathematical model on the force and torque moments is presented using numerical integration method based on differential geometry theory. The calculations of the force and torque moments of the twin-screw kneader are given. The static load calculated by the method presented is inclined to be conservative compared with the traditional methods and the results can provide theoretical basis for the strength calculation of screw rotors and the bearing selection.The high-performance and high-precision machining is the key technology of the screw rotors for differential twin-screw kneader. After analyzing the current manufacturing technology status, form shaping grinding method is presented based on superhard tool materials diamond/Cubic Boron Nitride(CBN). The theories on solving form shaping tool are established using space gears engagement and differential geometry theory. The contact properties between the helicoids and the shaping tool are analyzed. Offset surface method is used to calculated the actual profiles of shaping tool. Smoothing treatment of the base body of CBN grinding wheel is performed using biarc spline method. The mathematical model of error analysis for CBN shape grinding maching of screw rotors is proposed. Influence curves of tooth errors with mouting angle error and mounting distance error as well as grinding wheel wear are presented. CBN grinding wheel trimmings for machining screw rotors are analyzed. The trimming errors using single diamond pen and diamond dressing gear are induced. The design of diamond wheel for CBN grinding wheel and the dressing characteristics are discussed.The mathematical models of milling and hobbing are established aimed at the high-performance and high-precision machining of screw rotors based on cemented carbide tool materials CBN and PCD. The mathematical model of figure shaping tool and hob accuracy design theories of axial section for screw rotors using engagement principles of helical gear drive based on multi-degree-of-freedom theories and normal method of space tooth surface are established, respectively. Above theories demonstrate the engagement features between the helicoids of screw rotors and the basic worm face of hob and provide a theoretical basis for other hob design method so as to lay a theoretical foundation by using reversible carbide tool.The requirement analyses, system structure, design and control flows of CAD/CAM system for differential twin-screw kneader are put forward. The key technologies on how to design the CAD/CAM system are analyzed. According to above design and machinine theories of screw rotors for differential twin-screw kneader, one CAD/CAM system using C# language and .NET framework which can be used to design, analyze and machine the screw rotors for differential twin-screw kneader is developed. Corresponding experiments using figure cutter and CBN grinding wheel for female and male rotors as well as precision measurement in three-Coordinate Measuring Machine (CMM) are performed based on the CAD/CAM system. The detection results show that the machining methods can meet the high-performance and high-precision requirement for screw rotors, colomn worms, helical gear, etc.