Statistical analysis of pressure fluctuations in paste extrusion

The pressure signals generated during the extrusion of paste through concentric dies were studied to determine if changes in paste structure could be detected from these signals. An instrumented strain frame was used to collect data from extrusion of a model alumina paste, solid soap and a viscous gel. Data were statistically analysed to define an index for quality of extrusion. Initial results indicated that the process related fluctuations were significantly larger than the machine noise and the major cause of fluctuations in ceramic pastes involved the yielding processes at the die entry. Experiments using pastes containing added inhomogeneities, laminations, different modes and extents of mixing all showed a correlation between the standard error in the filtered signal and the physical effect.