Single-screw Extruder Machine Mixing Process Characterization Study

Single screw extruder is often used for polymer mixing, the effect of which is critical to the quality of the final product. Thus it is of great importance to study the mixing behavior of melt polymer in single screw extrusion.Based on the analysis of the deformation gradient tensor and Green deformation tensor in the mechanics of a continuous medium, the present paper introduces "Deformation Measure" (M) as a new deformation measure for polymer mixing in screw extrusion processes. In contrast to previous strain measures heuristically proposed by Mohr, et al., Mckelvey, and Pinto and Tadmor, the newly introduced parameter M can naturally incorporate the demixing phenomena and systematically take into account the three-dimensional circulatory flow with the screw flight effect. Therefore M can be regarded as an improved strain measure. "Weighted Average Deformation Measure"(WAM) as a quantitative measure is also proposed to indicate the overall deformation characteristics to the "goodness of mixing" of the extrusion processes. The present paper first discusses the delicate differences between M and several other strain measures in case of the two-dimensional velocity approximation including several different screw parameters and operating conditions such as helix angle and pressure gradient.Then the paper discusses the application of M into a general three-dimensional velocity field obtained by a three-dimensional finite element analysis(ANSYS) of extrusion processes. In determining WAM in the three-dimensional application, the residence time distribution function, including the three-dimensional circulatory flow effect is used.