The Net Normal Force Per Crossing Point: A Unified Concept for the Low Consistency Refining of Pulp Suspensions

Abstract

The objectives of this article are:

– First, to theoretically propose a unified concept: the net normal force per crossing point,

– Second, to experimentally undertake refining trials on a pilot disc refiner in order to compare all concepts for the refining intensity and to validate the chosen one.

We will begin by re-visiting the old concepts of the refining intensity, in the low consistency regime. After a theoretical proof based upon the physics of the phenomena, applied to beaters and industrial refiners, a unified concept of the refining intensity is proposed and strengthened: the net normal force per crossing point.

Then, experimentations are undertaken on a pilot refiner (single disc) in hydracycle (or batch) conditions. More precisely, the effects of the grinding codes and of the average crossing angle of the bars are analyzed in a set of 6 refining trials. For these experimentations, different engineering concepts of the refining intensity are compared (specific edge load Bs, specific surface load SSL, modified edge load MEL, net tangential force per crossing point and net normal force per crossing point). These refining intensities should allow to analysing the cutting kinetics of fibres.

All the chosen engineering concepts reach this goal more or less however the net normal force per crossing point is the best tool. Indeed, through the range of the data concerned, it revealed a clear monotonous evolution with the cutting kinetics on fibres. The more is the net normal force per crossing point, the more is the cutting effect on fibres.