Adaptation of in-line ultrasonic velocimetry to melt flow measurement in polymer extrusion

Pulsed wave velocimetry (PWV) is an ultrasonic technique for measuring velocity profiles in flowing liquids. In capillaries, PWV requires using ultrasound transducers with high center frequencies and a large bandwidth. This type of transducer is restricted to operating temperatures below 50 °C. However, in polymer extrusion, velocity profiles of flowing liquids with temperatures up to 250 °C are of interest. This contribution describes the development of a new ultrasonic measurement tool, which is fully integrated in a heated capillary die. It enables long-time measurement of the extrudate using the buffer rod technique and active cooling. The developed prototype was successfully validated in an extrusion experiment: the velocity profile of glass-fiber-filled polypropylene was measured immediately after extrusion in a capillary die.