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Presenter: Peter Wild - Department of Mechanical Engineering, Queen's University
Supervisor:

Date: Tue, February 19, 2002
Time: 11:00:00 - 12:00:00
Place: EOW 430

ABSTRACT

Abstract:

Mechanical refiners are commonly used in the pulp and paper industry to reduce wood chips to fibres and to develop the properties of fibres to be suitable for papermaking. Most refiners consist of plates, with patterns of bars and grooves on their surfaces, mounted on opposed discs. In some cases, one disc rotates and the other is stationary. In other cases, the discs counter rotate. Chips and pulp flow radially through a refiner and are repeatedly compressed and sheared between the bars of opposing plates as these travel past each other. The relative magnitude of shear and normal forces, the rate of application and removal of these forces and their distribution over the surface of the refiner plate all affect the properties of the pulp that is produced. If these forces could be measured directly, this information could be used to develop control strategies for refiners that would provide tighter control on the quality of pulp and, therefore, the quality of paper production.

In the current research, a novel piezo-ceramic sensor been designed to measure the shear and normal forces applied to a short segment of a refiner plate bar. The sensor base is mounted to the back of a refiner plate and the tip replaces a short segment of a refiner plate bar. Critical aspects of this design include isolation of shear and normal force signals and the frequency response of the sensor, relative to the bar-passing frequency of the refiner. A first generation prototype was fabricated and tested in a laboratory-scale atmospheric-discharge refiner. This prototype has made the first independent measurements of shear and normal forces in an operating refiner.

Based on this success, a second generation prototype has been developed for application in a pilot-scale refiner which operates at elevated temperatures and pressures. These high temperatures present new design challenges including selection of suitable piezo-ceramic materials and the effect of differential thermal expansion of piezo element preload. This second generation sensor has been commissioned in the laboratory-scale refiner and will shortly commence trials in the pilot-scale refiner.