Characterization of Kneading Block Performance in Co-Rotating Twin Screw Extruders

Abstract

In this chapter, the image analysis and visualization methods are used to ascertain the flow and mixing behavior in the kneading blocks. The paper quantitatively relates the influence of kneading block configuration and operating conditions to the mixing performance. The purpose of the chapter is to provide evidence, elucidating what occur in kneading sections. It also bridges the understanding of the flow and mixing behavior in mixing section to the final morphology. The co-rotating twin screw extruder is an important processing machine in polymer industry. The degree of mixing in an extruder is one of the most significant issues affecting the processability, productivity, and final properties of products. Residence time distribution and flow visualization are two common experimental ways to investigate mixing in a complex flow field. It is difficult to predict the complex flow patterns and mixing performance due to complex screw configurations of kneading sections inside an extruder. The complex rheological properties of polymeric materials further complicate the analysis of flow and mixing. The relationship between the final morphology of an extrudate and the mixing performance in the kneading blocks is still poorly understood. Computational simulations still lack the confirmation of experimental evidences. Finally, it is not realistic to measure experimentally the entire velocity profile in the kneading sections. All these factors lead to the need for some simple method to determine key aspects of the flow through complicated mixing sections.