In-process density control of extruded foam PVC using wavelet packet analysis of ultrasound waves
Ultrasound waves (UT) propagating at a frequency of 2.25 MHz through the melt flow inside an extruder die were used to monitor the density of the foam extrudate. Acoustic properties of the polymer melt, manifested by the behavior of the ultrasound waves inside the die, were empirically correlated to the density of the extruded foam. Wavelet packet analysis was used to filter the ultrasound echo signals. A three layer multi-layer perceptron artificial neural network was used to correlate the response of the ultrasound sensor to the measured foam density. The density of the extruded foam was varied by varying the processing conditions over a wide practical range. The experimental work shows a strong correlation between the acoustic properties of the polymer melt inside the extrusion die and the resulting foam density. A strong correlation was obtained by using the filtered ultrasound waves using wavelet packet analysis. (C) 2002 Published by Elsevier Science Ltd.
density pvc wavelet ultrasound extrusion ann