Construction of a single bar refiner

Abstract

The target of this thesis work was to construct a laboratory scale low-consistency refiner by modifying an existing design to enable more realistic refining conditions. The aim of the modification was to be able to study refining energy and forces affecting fibres more closely, particularly enabling the determination of bar coverage and pulp consistency in the gap by image analysis. The designing and construction of a pulp flow system for the refiner unit was also an important part of the thesis. Setup and testing of a system for imaging fibres in the refining gap was realized.

The modification of the original design was made by designing a new stator bar with dimensions similar to the rotor bar. The purpose of this design was to create more realistic conditions during refining. This design was first tested with the original stator bar by machining it with a groove similar to the one in the rotor bar, and later constructing two additional bars to reach the desired smaller gap size. The pulp flow system was designed and constructed to enable even flow conditions for the refiner unit. The installing and setup of the laser illuminated imaging system was conducted to enable image capture of the refining phenomena.

Some problems were encountered during the course of this work. The errors in measuring the original gap size resulted in wrong dimensioning of the new stator parts. For this reason some modifications had to be made afterwards to reach the targeted gap sizes. The pulp flow system was constructed without any major issues, but problems with the refiner unit clogging when operating with pulp consistencies > 2 % left some room for improvement. The imaging system installation and preliminary trials were successful, resulting iii some good images from the gap between the rotor and stator bars. Images showed e.g. that bar coverage is clearly not 100 % at 2 % pulp consistency with 150 µm gap size, and that there is potential in developing the image analysis method aiming to determine bar coverage and pulp consistency in the gap. The target of the thesis to construct a research tool for refining studies was achieved