The application of stress may cause the liquid component of a paste to move through the solid matrix. Small changes in liquid content can lead to significant changes in flow behaviour and product properties. The liquid maldistribution arising during the flow of a paste from a barrel through a die has been studied experimentally. Measurements by means of sectioning, weighing and drying indicate a non-uniform liquid distribution of the paste in the barrel. There are three distinct regions including an inner region along the axis and also an outer region near the barrel wall where there is a lower moisture content. At the wall itself, a very thin layer of liquid is believed to exist. These are separated by a third region, an annulus of higher moisture content. It is shown that this liquid maldistribution is affected by the velocity of extrusion. The moisture content of the barrel paste and the extrudate decreases as the extrusion process proceeds.
- Moisture content