LC - Beating of Pulp Fibres, 1999 Pulping Conference Proceedings

Tom Lundin

Bruno Lönnberg

Åbo Akademi University

Laboratory of Pulping Technology

Kimmo Harju

Petteri Soini

Sunds Defibrator Valkeakoski Oy

This paper describes a method for evaluating the beating from process variables: net motor load, rotational frequency, mass flow and stock consistency. It was prepared to establish some correlations between general beating conditions and pulp rheology, as well as beating results. A load-production graph was developed for this purpose. Beatings with long-fiber ECF and TCF-bleached kraft pulp were performed in a modern conical refiner, and data from the results were applied for evaluations based on this method, which was developed in our laboratory.

The result of the beating process is considered highly dependent on the number of impacts on the fibre. In addition, the intensity of impact determines the beating effects on the fibres, i.e. fibrillation and cutting. The resultant beating effect on the fibre, accordingly, is dependent on its time of residence in the beating zone, and the disc gap and rotational speed, which affect fibre compression and shearing respectively. Expressed as beating process parameters, pulp flow, consistency and beating zone length describe the time of residence or the number of impacts. The intensity is described, as mentioned above, by the disc gap and rotational speed, or preferrably, by the impact forces, i.e. net motor load. For common evaluations of the beating process a simple model was developed, including net motor load, rotational speed, pulp production (flow), consistency and refiner design.

The beating results - evaluated from a rheological approach- indicate that beating under constant conditions (pulp grade, consistency, rotational speed, specific energy consumption) changes the operational point from low net motor load and low pulp production to high load and high production, if the specific edge load is increased. The same is true if the fillings are changed from broad bars an long impact length to narrower bars and shorter impact lengths. Beating results showed ordinary development of fibre and stock properties during processing. ECF beating at higher rotational speed resulted in fiber straightening as well as slower freeness and strength development.