Design of Plastic Machine Screws using FEA

Abstract

Many theoretical, experimental, and simulation studies have already described the polymer behavior in Extrusion process focusing on the polymer flow inside the barrel. However, the mechanical behavior of the screw shaft itself during extrusion does not draw much attention, although non proper design and selection of this device, which is present in large part of industrial processes, could mean poor performances, excessive power, severe wear of screw and degradation of the conveyed material. The present work aims to investigatethe performance of various types of screw under different working conditions. Finite element analysis is used to master a technique to evaluate the radial displacement of the used screw, while analytical solution is used to clearly describe the polymer behaviour affecting the proposed screw.The screw parameters are its feed zone length and compression zone length, while the axial pressure, temperature profiles and screw speed are the main parameters considered in processing the desired polymer. The pressure profile along the length of the extruder reaches a maximum close to the end of the compression section of the screw. Sharp pressure peaks occurred at low speeds for the traditional screw case, while being at the high speed range for the rapid compression screw case. The temperature profile along the screw is affected by the set temperature of the metering section heater. The minimum displacement occurred at the metering zone, while the maximum displacement occurred at the feed zone moving to the compression zone for traditional screw. Pressure has little effect on the screw displacement ranging from 5 % to 10 %, while temperature has the major contribution in screw displacement. Screw displacement could be decreased by screw cooling of the feed section,reduced temperatures in the metering section, andincreasing clearance in the feed throat region.