Research On Polymer Composites Dynamic Extrusion Process In Triple-screw Extruder And Its Structural Performance

Polymer composites have been widely used in different fields such as aerospace,automotive, electronics, electrical, construction, medical equipment, home appliances, andpackaging, and the market demand for it is increasing in recent years. However, thepreparation equipments of polymer composites are mainly single-screw or twin screwcompounding extruders, these traditional devices have a number of disadvantages: poordispersion, high energy consumption and low product quality. We propose and invent thatline-shape arranged three-screw extrusion mixing methods and techniques with a vibratilemiddle screw, which provides a new means for the preparation and processing of polymercomposites, and it has very important scientific and practical significance on the applicationand development of polymer composites.Through the synergies between the distribution of tri-screw power transmission,electromagnetic exciting force and the extrusion system mechanical structure, the axialmeshing gap between the main screw and both sides of the vice screw changed periodicallythrough axial vibration of the middle the screw, and the vibration force field was brought intothe whole mixing and plasticizing process of polymer composites, and the line-shape arrangedthree-screw dynamic mixing extrusion was successfully developed. In this paper, axialvibration dynamic model of the middle screw was established and its amplitude-frequencycharacteristics in the damping system were analyzed. Trough Tanner’s amendment Maxwellnonlinear constitutive equation, a three-dimensional numerical simulation of flow ofthree-screw C-type groove indoor materials was accomplished, which proved that axialvibration of the middle screw takes profound effect on melt mixing and process of extruding,and found that the vibration force field led the C-type groove indoor materials to producechaotic mixing phenomenon, proposed and defined a dimensionless combinatorial number(quasi-number VI1) as an index to indicate the extent of strengthening mixing and dispersionof materials by the vibration force field.In this paper, we established physical and mathematical model of three-screw extruderwith a vibratile middle screw. By using overlapping grid technique, we simulated andanalyzed the relationship between melt velocity, pressure, viscidity and shearing velocity andscrew speed, the middle screw vibration frequency or amplitude. The results showed that theflux, velocity, shearing velocity increased with the increasing of the screw speed, vibrationamplitude and vibration frequency. However, the average viscidity, pressure decreased atsome degree. And the pressure inside the flow channel and the shear rate varies periodically. Obviously, mixing function was improved when increasing the screw speed, vibrationamplitude and vibration frequency. This proved that the vibration of the middle screw couldstrengthen the mixing process and enhance the product performance of polymer composites.Using self-developed line-shape arranged tri-screw dynamic mixing extruder, weprepared EPDM/PP, wollastonite/polypropylene and ultra-fine calciumcarbonate/polypropylene three typical polymer composites. The experiments which changethe vibration parameters (vibration frequency and amplitude), screw speed and filling ratiofocused on the inherent law between the tensile strength, impact strength, fracture elongation,phase structure with vibration parameters. Results showed that comparing with steady state(without the vibration force field), the mechanics properties of composites produced byvibration extrusion were improved at different degree and the material had excellentmicrostructure. Meanwhile, the results verified the introduction of vibration to the middlescrew could improve the structural behavior and quality of composites and the machine isideal for the processing and preparation of polymer composites.