Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on July 14, 2009). Includes bibliographical references.

This work investigates the behaviour of clay in a commercial screw driven extruder used to manufacture clay drainage pipes.  Based on a striping effect observed within the clay during extrusion, experiments and models have been constructed to determine if these stripes can be removed.  The aim is to improve product yield and reduce waste. During the course of this work, it will be described how it is believed that the stripes are the result of localisation and shear banding which allows water to evaporate quicker from some areas than others, causing stripes.  Some preliminary work is discussed regarding a hopper, used as a step towards generating models for the extruder.  Latter sections detail the models created using various mathematical techniques which are used to simulate the material as it flows through the system.  Of particular relevance is optimisation theory which allows various parameters to be determined based on a pre-determined function and a set of initial guesses.  Building upon this work leads to the conclusion that modifying the design of both the auger and extension can reduce the chances of localisation, thereby reducing the chances of stripes forming. Finally, a set of recommendations are made regarding potential design changes, and a complete redesigned system is proposed as an example of what would be required.