Vibrating Force Field Of Plastic Extrusion Process Mixing Mechanisms

As a result of its unsophisticated performance, mono-polymer is not able to satisfy the using requirements of various products and particular demand of certain moulding methods. And with many other factors, such as the polymer's serious aging, high price and cost, it is generally necessary to append auxiliaries and mix in order to acquire uniform composite materials, which can improve the products'operating properties or reduce its cost. The mixing capability of polymer moulding devices is in direct connection with the quality of polymer production and determined by blending mechanism.There are at present two main researching trends according to the vast investigations conducted on the processing mechanism of polymer extrusion molding. One is changing the structures of the present molding machines to develop new type mixing elements, such as barrier screw extruder, twin-screw extruder, multiple-screw extruder, Buss mixer and twin-rotor mixer. Another trend is to improve the operating condition of the improved extruders, for example, the leading extruders——the high speed extruder and the electromagnetic dynamic plasticizing extruder.The primary aim of this thesis is trying to integrate advantages of the two research methods. On structural development, new series disc mixing device is designed based on elongation flow theory. And on the other hand, vibration force field is introduced into the common screw, the pin screw and the disc screw milling devices. Meanwhile, numerical simulation is conducted on each simplified mixing section model under vibration force field, and comparative analysis is carried out on how the different vibration parameters affect the blending mechanism and the plasticizing performance of the mixing devices.The simulations show that vibration force field with proper vibration parameters can make the mixing devices have longer residence time, smaller segregation scale and higher instantaneous efficiency of stretching, promote the plasticization process, actualize the dynamic variation of every physical quantity, and improve the mixing mechanism of the plasticizing extruder. Compared with steady processing conditions, small vibration amplitude and frequency value have little impact on each physical quantity, whilst large value has greater impact. However, it doesn't mean the larger the parameters, the better the plasticization. There exits best interval for the frequency and amplitude of vibration.The above result comes from the 3-D isothermal simulation only on one section of the entire mixing device. There is really much room for doubt about the fact that whether the simulation conclusion from local section can reflect the mixing property of the whole blending equipment. Consequently, it is essential to undertake further research on the following aspects so as to better the numerical simulation and to provide reliable information for industrial application:(1) Build a three-dimensional non-isothermal model on the whole mixing screw, and take into account the temperature.3-D simulation on the entire screw is necessary as well as the temperature. The emphasis is the investigation on creep, stress relaxation, lagging, internal friction, and so on, which reflect the viscoelastic behavior in polymer melt.(2) Establish a continuous model on vibration parameters and analyze the effect of vibration force field parameters on the milling mechanism and modality for mixers and accordingly avert the drawback that happens when discrete vibrant amplitudes and frequencies are used for numerical simulation.(3) Found a compositive model on blending facility. In a compositive model all-sided consideration should be given to the physical chemistry parameters of blending facility, barrel and other parts, together with the polymer melt parameter. Relative to the idea that only the size information and melt parameter are taken into account, the above attempt may educe realer and more practical results.