Method and apparatus for making measurements related to the first normal stress function of viscoelastic fluid material

摘要

The first normal stress function of a viscoelastic material which is a measure of its elasticity and a more sensitive indication of certain other parameters of the material, and process conditions, than the viscosity thereof, is determined from measurements of the thrust in a direction normal to the inner and outer walls of an annular channel in which the viscoelastic fluid material flows under pressure, at high shear rates in an angular direction. These thrust measurements may be made under regulated flow so as to eliminate the need for alignment of the positions at which the thrust measurements are made. The measurement system is closed so that evaporation and degradation of the fluid material as may occur in such systems as are open to the atmosphere are avoided. The first normal stress function may be determined over a broad range of shear rates such as are experienced in polymer processing (e.g., extrusion and injection molding) so as to facilitate continuous or real time process control.