Abstract
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.
A demonstration of the striping effect is provided alongside a discussion of the extrusion equipment. Methods that can be used to model the existing system are discussed with reference to both kinematics and statics. Various mathematical tools are described including the right conoid approach used to generate a helix. Discussion also takes place on material yield criteria, methods for determining material behaviour and the use of a parameter defined as b which can be used to determine localisation. 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 of this work 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 predetermined 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. A complete redesigned system is then proposed as an example of what would be required to improve the existing system.
A demonstration of the striping effect is provided alongside a discussion of the extrusion equipment. Methods that can be used to model the existing system are discussed with reference to both kinematics and statics. Various mathematical tools are described including the right conoid approach used to generate a helix. Discussion also takes place on material yield criteria, methods for determining material behaviour and the use of a parameter defined as b which can be used to determine localisation. 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 of this work 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 predetermined 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. A complete redesigned system is then proposed as an example of what would be required to improve the existing system.
| Original language | English |
|---|---|
| Publisher | University of Aberdeen |
| Number of pages | 288 |
| Publication status | Unpublished - 2009 |
Bibliographical note
A thesis presented for the degree of Doctor of Philosophy at the University of Aberdeen by Matthew J.S. Kite (MEng University of Aberdeen)Keywords
- pipe, clay mathematical models
- pipe, clay computer simulation
- pipe, clay design