A Study On The Single-screw Precise Extrusion Mechanism

Based on polymer processing rheology and single-screw extrusion theories, theprecise extrusion theories and techniques were investigated in present paper. My research works include 9 parts and as follows: 1. Based on the materials science and single-screw extrusion theories, a ParallelPressure Stabilization Apparatus (PPSA) for single screw extruder has been studied,which has many advantages, such as, simple construction, convenient to clean up,without the problems of melt leaking, and perpendicular arrangement of the PPSA withthe extruder die. 2. A mathematical model of PPSA for single screw extruder has been establishedbased on the assumptions of power law fluid and isothermal process. Numericalsolutions for the model were carried out with the help of MathCAD. The influences ofgeometrical and technological parameters on the stability of extrusion pressure andoutput with specified pressure fluctuant pattern at the end of main screw were studied.The simulation results indicate that when the screw speed of PPSA is fixed, the pressureand output fluctuation of extrusion can be compensated up to 97.6% with automaticregulation of filling length of the polymer melt in the barrel. If the screw speed ofparallel pressure stabilization apparatus is varied corresponding to the pressurefluctuation, the pressure and output fluctuation of extrusion can be fully compensated. 3. Simulated computation has been done for PPSA for single screw extruder, whenscrew is considered as a parallel flat flowing path and polymer melt is Newton fluid.The results show that by changing the screw speed, the pressure fluctuation can also becompensated up to 83.63%. 4. The flow field of the polymer melt has been researched in typical extrusionchannel. The constitutive equations of viscoelastic fluid were introduced in themathematic model for simulating the flow in parallel flat channel and the model wassolved with the help of software MathCAD. The results shows that die pressure ofextruder, relaxation time of polymer and geometrical parameters of die have significanteffect on stress tensor in extruder die. By changing the geometrical parameters in theflowing channel, the pressure can be controlled. 5. The simulation of pressure, temperature distribution in different zones in preciseextruder has been researched. 6. A program for on line recording and displaying extrusive output for preciseelectronic balance has been designed, and has been used in the process of dynamicextrusion, which increases the record precision. 7. Two stable dynamic mathematic models of extrusion have been created, whichhave some relation with times, by using the experiment data of extrusive processing ofinstability. This model can reflect the change process of two stable states in realextrusion. III北 京 化 工 大 学 博 士 学 位 论 文 8. The sensitivity of melt polymer viscosity to temperature, shearing stress andstress action time has been reflected, the effect of stress history and deformation historyand heat history of polymer to melting process has been researched, and swelling andradio distortion and flow instability and wall slip. 9. The effect of polymer pressure, temperature, screw speed and geometricalparameters of screw and geometrical parameter of die flowing channel, as well as solidconvey and solid bed broken on the stabilities of extrusion process has been concluded,which provides important reference data for design of precise extrusion equipment andparameter control of precise extrusion process.