Forces on bars in high-consistency mill-scale refiners: Effect of consistency

Abstract

The contact mechanics that arise during bar-crossing impacts are responsible for inducing the stresses, and corresponding strains, that develop raw wood fibre into useful papermaking pulp. Enhancing our knowledge of the interactions that make up these impacts, and how they are affected by process variables, is therefore a necessary step to advancing refiner technology. Experiments by Senger and Ouellet [1] involving individual fibre bundles, or flocs, in a single-bar refiner have indicated that bar forces are dependent on floc consistency, floc grammage and bar edge sharpness. These results offered insight into previously unexplainable behavior, but investigation of these relationships in mill-scale refiners was restricted by lack of available measurement technology. This investigation is now possible with the development of a refiner force sensor (RFS) that replaces a small segment of refiner bar, and is capable of measuring normal and shear forces experienced during individual bar-crossing impacts. Bar forces from RFS tests in two mill-scale refiners under nominal operation have already been reported [2]. During the same installations, consistency within the refining zone was also varied in individual experiments. The principal goal of this work is to report on the effects of refining consistency on recorded bar forces in these two trials.