Study On Energy Consumption In Polymer Plasticizing And Conveying Process Based On Elongation Rheology

At present, screw machinery is widely used for processing polymer materials. Polymerplasticizing and conveying process in screw machinery is implemented by shearing anddragging forces acting on materials which are generated by screw rotation, and large amountsof energy is consumed in the process. In addition, there are some ubiquity disadvantages withtraditional equipment, such as highly depending on the properties of materials and longthermo-mechanical processing. The operating principle and the working process of theequipment of polymer processing based on extensional rheology are completely different thanthat of conventional screw machinery. The novel equipment can help to resolve the problemof long thermo-mechanical history of materials and high energy consumption in polymerprocessing from the level of polymer plasticizing and conveying mechanism. The study ofpolymer plasticizing and conveying process based on extensional rheology and energyconsumption in the process is very important and practical for the development andimprovement of polymer processing theory based on extensional rheology.Vane plasticizing and conveying unit (VPCU) is the basic unit in polymer processingmachine based on extensional rheology. In this paper, the whole plasticizing and conveyingprocess of polymer in VPCU include solids conveying, melting and melt conveying process isstudied systematically for the first time. Energy consumption models of three sections in vaneextrusion system are developed based on the study of polymer plasticizing and conveyingmechanism in VPCU.In this paper, the physical and mathematical model of polymer solids conveying in VPCUis developed, then further the characteristic function of pressure in the chamber of VPCU andthe characteristic function of energy consumption in solids conveying process are obtained.The research shows that the volume of the chamber changes periodically, enormous pressurecan be built in the chamber and thereupon polymer solids is rapidly compacted when thevolume decreases. Energy consumption in polymer solids compacting process is influencedby geometric parameters of VPCU, density of the material, frictional coefficients between thematerial and surfaces of VPCU, and so on.Through building the physical and mathematical model of polymer melting in VPCU,energy consumption characteristics in melting process is analyzed in this paper. The researchshows that the material enters into melting process in advance because it is compressed tightlyin solids conveying process. Heat transfer between the stator and solids is strengthened whenthe volume of the chamber decreases and it can help to accelerate the melting of material and reduce the energy consumption in the melting process. Energy consumption in polymermelting process in VPCU is proportional to the rotational speed of the rotor because thechamber of VPCU has completely positive displacement characteristics in material conveyingprocess.The physical and mathematical model of melt conveying in VPCU is also developed. Theexpressions of velocity distribution and pressure distribution in the chamber of VPCU areobtained, and then further the model of energy consumption in melt conveying process isdeveloped. The results show that melt endure elongation strain both in the axial and thecircumferential direction in the chamber, and a normal stress field in the axial directionformed in the chamber can help to convey the melt with positive displacement and notdepending on the properties of the material. The energy consumption in melt dischargingprocess accounts for a major part of total energy consumption in melt conveying process. Theenergy consumption is proportional to the rotational speed of the rotor and it increases withincreasing output pressure of the chamber and increasing viscosity of the melt.Finally, energy consumption characteristics in polymer solids conveying process, meltconveying process and the whole plasticizing and conveying process including solidsconveying, melting and melt conveying in vane extrusion system have been studiedexperimentally by means of the visualized vane experimental device and the vane extruder.The experiment results are consistent with the predictions of energy consumption models.The method and equipment of polymer plasticizing and conveying based on elongationrheology is a completely new theory and machinery for polymer processing. The proposedmodels of polymer plasticizing and conveying process in VPCU and the energy consumptionin the process laid a good foundation for further study of polymer vane plasticizing extrusionprocess and its mechanism. This study provided an important theoretical basis for thepromotion of the vane plasticization equipment for polymer processing.