Acoustic sensor for in-line monitoring in polymer extrusion dies

We present a pressure-wave-based acoustic sensor device for inline monitoring of polymer flow behavior. The device is made to be integrated in a slit capillary of an in-line-extrusion-rheometer, but could be implemented in any die used for extrusion. It was manufactured to withstand the high pressures involved in the extrusion process by employing a boundary reflection based acoustic measurement to determine the viscosity of the polymer. A high temperature graded PZT disc transducer was used and the whole system was designed to measure viscosities at the temperatures of the extruder without the need for external cooling of the PZT element.