Experimental analysis of the residence time distribution in a single screw rubber extruder using a digital image processing method

Abstract

With the ongoing digitalization in the industrial sector, also called Industry 4.0, automation techniques promise huge potential for the rubber industry. Advanced automation methods allow for precise control of the extrusion process and improve the consistency in product quality. Since product quality is affected by process parameters in a complex way, predicting the flow conditions and the mixing in an extruder is a prerequisite for more sophisticated Industry 4.0 applications. These Industry 4.0 applications hence require for short computing times and thus sufficiently fast models for implementation in production systems. A useful measure for the flow inside the extruder is the residence time distribution (RTD). It enables an analysis of the residence time of the material particle in the process and subsequently a statement about the homogenization characteristics. For the investigation of the RTD and the effect of process parameters on residence time characteristics, a single-screw rubber extruder equipped with a gear pump was considered. In this work we present a method to identify the RTD for a certain compound using experiments. We describe an experimental procedure with a special tracer material and a modified image processing method to detect the RTD. To validate the method, the experiment was repeated and compared in a predefined reference state. The RTD curves are then used to identify effects of process parameters on the throughput behaviour of the extrusion process. Based on the results we discuss how the RTD can be used to interpret the flow conditions and the mixing behaviour inside the extruder.