First Steps in Design Analysis and Troubleshooting Single‐Screw Extruders: Identifying Common Causes of Gels and Black Specks, Utilizing Metering Channel Flow, Pressure Drop, and Temperature

When evaluating single‐screw extruder design and troubleshooting in plant settings, many times the production issue is black specks and gels in the product. It is necessary to determine if the metering section of the screw is in control by accurately predicting the flow rates. The metering section temperature calculation is accurately predicted to determine polymer viscosity. These calculations are strongly affected by the screw channel depth, the role of the different components of the screw, and the shear thinning characteristics of the polymer. It is a goal of this paper to bring these issues together in one publication so the practitioner may determine how he/she wishes to proceed as a design evaluator or troubleshooter. The historic Barrel Rotation theory is compared with Screw Rotation theory for polymer flow and temperature rise, documenting analysis tradeoffs. The issue of how polymer shear thinning affects the predictions of flow and pressure drop in the screw metering section is also addressed. A set of experiments on a specially designed glass‐barrel extruder should help the troubleshooter understand how each element of the screw affects the pumping capacity and their effect on predictions of screw residence time and chaotic mixing.