LIQUID MIGRATION IN PASTE EXTRUSION

The flow of paste can be substantially controlled by the internal movement of the lubricating liquid phase although the effects are as yet not well understood. Here, experiments have shown that due to liquid movement, exposure of extrusion pastes to load over short periods of time of the order of an hour can increase the extrusion pressure by a factor of 15. This effect depends upon both compression stress and time. Theories from soil mechanics based on Darcy's law do not adequately describe the behaviour, probably due to complications arising from the properties of the components essential in the paste mix. These experiments form the basis for a new standard test which will aid in the design of good extrusion pastes.