Construction of a single bar refiner

We constructed a laboratory scale low-consistency refiner (single bar refiner) station to study refin- ing energy and forces affecting fibers more closely. The specific aim was to enable measurement of fractional bar coverage and pulp consistency in the refining gap by using laser illuminated imaging equipment and mathematical image analysis. The construction of the single bar refiner included designing stator bars with dimensions similar to the rotor bar. This design created more realistic conditions during refining, and the design was tested by using three different bar setups to reach the desired gap sizes. The pulp flow system was designed and constructed to enable even flow conditions for the refiner unit. The imaging system installation and preliminary trials resulted in sharp images from the refining gap between the rotor and stator bars. Images showed that bar coverage was clearly not 100% at 2% pulp consistency with 150 μm gap size. There was a clear correlation between suspension consistency and the bar coverage. The preliminary trials demonstrated the promising potential of the device, as well as some improvements needed in monitoring and image analysis methods. Increasing refining consistency would increase the amount of fiber inside the gap between the rotor and stator bars. Also, the gap is not fully covered with fibers during refining. Application: Better understanding of the factors that affect fiber distribution and coverage in the refining gap can lead to greater energy efficiency in the use of low-consistency refiners.