A Model for Feeder-Extruder Interactions

Abstract

In the field of plastic extrusion, the accurate feeding of materials to the extrusion process is an important issue. The end product quality is partially dependent upon the extruder receiving feed materials in the correct proportions. Therefore, the understanding of the relationship between the feeder and the extruder is very important. This paper presents and analyzes this relationship. The feeder is usually a separate and distinct item from the extruder. The feed materials and the environmental conditions may affect the flow rate of the reaction or blending process of the extrusion process. The variation of this feed material may cause the quality of the overall product to be beyond an acceptable quality. This paper shows that two feeder parameters, the period and amplitude of the feeder error, affect the composition of the materials throughout the extrusion process. Understanding the effect of these parameters will allow for the overall improvement in product quality. This paper also shows that the extrusion process is able to dampen the error of the feeder. In other words, by mixing a fluid element the average fluid composition will tend towards a nominal value. The fluid composition error associated with the fluid element will decay exponentially. This paper presents two models to describe phenomena described above. The first model is a theoretical description of an idealized mixing process with a time varying feeder error. The second model is an iterative mass transfer model representing a nonintermeshing twin screw extrusion process. An analysis of each of these models will demonstrate how the error of fluid composition reduces as a function of the amount of mixing.