A Conveying Model of Fluid Partially Filled in a Nontwin Screw Extruder Allowing for a Positive Displacement

Fill degree is a key parameter impacting twin screw extruders' (TSEs) mixing performance and melting behavior. The conventional conveying model of partially filled fluid relies mainly on empirical methods. A nontwin screw geometry introduces a speed difference between the two intermeshing screws to change the conveying means, and this speed difference offers a challenge for establishing a new conveying model. A visualization prototype with a global transparent barrel was developed in this article with carboxymethylcellulose sodium solution used as working fluid. Fill length was measured under different outputs and screw rotation speeds in a nontwin screw channel versus a corresponding twin screw channel; thus, fill degree was obtained using the observed fill lengths and nontwin screw geometries. A new conveying model of partially filled fluid was proposed which isolated positive displacement flow as an independent factor, and visualization observations revealed that due to differences in screw flight width, the positive displacement flow in a nontwin screw channel is larger than that in a traditional twin-screw channel. Results showed that dimensionless positive displacement conveying increased linearly with fill degree for a non-TSE geometry while it was independent of fill degree for a TSE geometry. POLYM. ENG. SCI., 2019. (c) 2019 Society of Plastics Engineers