Measurement of Unwanted Powder Build-Ups in Manufacturing Using High Frequency Ultrasonic Bursts and Standing Waves Reflectance Method

This paper proposes a combination of high frequency ultrasonic techniques to characterize non-invasively the thickness of unwanted powder build-ups that occur in pipes and charge hoppers during industrial processes. Three compressed iron oxide powder cakes were reproduced in laboratory in different thick-nesses varying from 5 mm to 15 mm. The density and hardness of the samples made in the laboratory were compared to samples that formed in-situ in a charge hopper using time of flight ultrasonic mea-surements, light optical microscopy, and pycnometer densitometry techniques. The powder build-ups were deposited on a metal plate instrumented with miniaturized ultrasonic sensors operating around the center frequency of 10 MHz. These sensors operated using both the reflection coefficient method-ology and a new standing waves approach. The thickness of the powders was measured by correlating the standing wave resonant frequency change to the quantity of powder deposited on the surface. The powder build-ups were also compressed using a pressure up to 15 MPa and the reflection coefficient and the frequency change using the ultrasonic reflectance method were used to decouple the effect of load to the thickness measurement. Build-ups of 5, 10 and 15 mm of thickness were obtained, and the ultrasonic method measured the layer thickness with an accuracy of 10 %. (c) 2021 Elsevier B.V. All rights reserved.