In-line flow measurement of molten PLA in capillary flow channels using ultrasound

Pulsed Wave Velocimetry (PWV) is an ultrasonic technique for measuring velocity profiles in flowing liquids. With an earlier prototype, we already demonstrated its applicability to monitor the flow behavior of molten polypropylene with different additives in capillary dies. In this contribution, we present an improved measurement setup, which allows testing liquids with temperatures > 220°C using a large bandwidth ultrasound transducer (UT). The UT works at room temperature and is acoustically coupled to the melt using a wave guide. The setup comprises active cooling and enables long-time in-line measurement. In this contribution, we show results obtained in-line during the extrusion of polylactide (PLA) with glass fibers at various feed rates. Using the acquired data, methods to calculate acoustical properties like the speed of sound and the damping in melt are discussed.