| The single screw extruder is the most useful piece of equipment used in the polymer processing industry. The solids conveying zone is an important section of the extruder, however, solid conveying has received less attention by extruder analysts than melting or pumping section. The lack of understanding for solid conveying was also caused by the unavailability of solids conveying rate data as a function of barrel and screw temperatures, screw speed, and discharged pressure. Developing a model capable of predicting the pressure and temperature profiles in the solids conveying zone accurately is crucial to develop a comprehensive model for the entire extrusion processing.;Friction forces between the solid polymer and barrel and screw surfaces play a decisive role in the solids conveying mechanism. Measurement of friction coefficient is an important part in modeling solids conveying. A new experimental device is designed to determine the dynamic friction coefficient of barrel, screw, and polymer surface under operating conditions found in the extrusion process.;Since almost all the previous model for the solids conveying zone are limited, a novel non-plug flow model was introduced to simulate the solids conveying. This model was based on bulk solid pellets mechanism and two-dimensional stress analysis. Two new parameters were introduced in this new model: internal friction force, and shear modulus. Taking into account the compaction behavior and dynamic coefficient phenomenon, this model could predict the behavior in the solids conveying section.;Finally, to verify the model, a special extruder that could measure solids conveying rate as a function operation conditions was built. Three shapes of PVC resin (powder, pellet, and flakes) were tested in this device. Different compressive situations, as well as different pressure build-up were found. Comparisons between Tadmor-Broyer model with lateral stress ratios and the new non-plug solid model show a more realistic behavior for the new non-plug model. |
