On the refining mechanism.

Application: A better understanding of refining mechanisms promotes more efficient refiner designs.

Improving the energy efficiency of thermomechanical (i.e. pressurized) pulp refining requires a good understanding of how fibers are refined in a disc refiner. This understanding would permit the refiner manufacturers to design refining systems that produce good quality mechanical pulp with reduced energy consumption. According to some published research works, the fiber movement in a refiner takes place along the fiber length. My recent study indicates that most of the fibers are rolled into strand-like aggregates, most of which are aligned approximately in the same direction. This suggests that a predominant rolling mode mechanism (across-the-fiber mode) prevails in refining.

The purpose of this investigation is to further elucidate the mechanism of chip refining by means of microscopic examinations of fiber aggregates collected inside a refiner and at the refiner discharge. The morphological and structural characteristics of the fiber aggregates of a thermomechanical pulp obtained in this study indicate a preferential radial orientation of fibers (mostly aligned parallel to the refiner bars) and a rolling mode refining. However, the fibers in immediate contact with the refiner bar surface are aligned in the direction of rotation due to the shear action generated by the refiner bars of the rotating disc.

This study reconfirmed the rolling mode of fiber refining theory. One oddity was that no mobile aggregates (which were not anchored onto the refiner bars) are found in the refiner gap in the refining segment. This problem may be attributed to residual steam flush action. The presence of "mobile aggregates" between the refiner plates would certainly be of great importance for better understanding the theory of' refining. Despite this, the proposed refining mechanism explains well the morphological and structural nature of the fiber aggregates at the refiner discharge.

Law is senior research associate, Pulp end Paper Research Center, University of Quebec in Trois-Rivieres, Canada. Address correspondence to Law by email at [e-mail]