Measurement of Forces on Refiner Bars for In-Process Detection of Fiber Cutting in Low Consistency Refining, 2016 International Mechanical Pulping (IMPC) Conference
Low consistency (LC) refining of mechanical pulp is more energy efficient than conventional high consistency (HC) refining. However, the degradation of mechanical properties due to fiber cutting at high refining energies has limited the widespread adoption of LC refining. Conventional strategies to avoid fiber cutting are based on postrefining measurement of pulp properties and, typically, this does not enable rapid adjustment of refiner operation in response to the onset of fiber cutting. The objective of this study is to detect the onset of fiber cutting by using custom-designed piezoelectric force sensors that measure shear and normal forces applied to pulp fibers by the refiner bars. Trials are performed in an AIKAWA/Advanced Fiber Technologies Inc. 16’’ single-disc LC refiner. The trials are run using mechanical softwood SPF pulp with 378 ml CSF at 2.5% and 3.5% consistency at rotational speeds of 800 rpm, 1000 rpm and 1200 rpm. Distributions of the peak normal and shear forces are determined for each operating condition and a two-parameter Weibull function is fit to each of these distributions. The scale parameter, which is one of three key parameters of the Weibull function, is calculated and length-weighted fiber length is plotted as a function of this parameter. The results show that the onset of fiber cutting consistently corresponds to a distinct transition in the plot of length-weighted fiber length versus scale parameter. This transition is believed to be caused by a fundamental transition in the fiber-bar interaction. This result suggests that these sensors have potential to be used for in-process detection of the onset of fiber cutting.
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