Maclin S. Hall

On-machine ultrasonic sensors for paper stiffness. Final report

This final report presents the results of a 5-year effort by the Institute of Paper Science and Technology (IPST) and its participating partners. The objective of this work was to develop and demonstrate sensors capable of measuring the velocity of ultrasound in the out-of-plane (ZD) and in-plane directions of paper as it is being produced on a commercial paper machine. On-machine ultrasonic measurements can be used to determine various mechanical properties of paper and to monitor process status and product quality. This report first presents a review of the background and potential benefits of on-machine ultrasonic measurements, then summarizes the results of previous work. The ZD measurement system involving the use of ultrasonic transducers in fluid-filled wheels is described in detail, including the method of measurement, the wheel mounting hardware, the on-machine operation, and an overview of the system software. Mill-trial results from two bump tests when producing 69{number_sign} and 55{number_sign} linearboard are presented. For the 69{number_sign} trial the correlation of ZD transit time with plybond and with ZDT (Z-direction tensile or internal bond strength) was greater than 0.8 (R squared). Also observed were ZD stiffness responses to refining and to calendering. ABB Industrial Systems Inc. was responsible for the in-plane sensor. A paper describing ABBs sensor and mill experience is appended.

THICKNESS DIRECTION MEASUREMENTS IN PAPER MATERIALS USING ULTRASONIC SENSORS IMMERSED IN WATER-FILLED WHEELS

A new ultrasonic technique aimed at simultaneously measuring the thickness and sound transit time in paper materials is presented. Two 1 MHz piezoelectric ceramic transducers immersed in water-filled rubber wheels are used to launch and receive signals transmitted through paper specimens inserted in the nip between the wheels. Time-delay analysis of the directly transmitted and rubber-paper interface reflection delayed signals provides the necessary information for thickness and transit time determination, from which the out-of-plane longitudinal sound velocity is calculated. Results are presented for paper grades from 50 to 1750 μm thickness.