ESTIMATES OF MAXIMUM HYDRODYNAMIC SHEAR STRESSES ON FIBRE SURFACES IN PAPERMAKING.

In the reported experiments, maximum shear stresses on the surfaces of pulp fibers have been estimated for flows in a typical paper machine and three common laboratory drainage testers. These surface shear stresses, which influence the retention of small particulate matter flocculated onto pulp fibers, were found to attain their highest levels in the fan pump, pressure screen, and in the drainage flows caused by table rolls. The Canadian Standard Freeness Tester and the Standard British Sheet Machine Produced shear stresses on fiber surfaces several orders of magnitude lower than those encountered in a typical paper machine. On the other hand, the Dynamic Drainage Jar was able to produce shears comparable to those found in high speed paper machines by suitable adjustment of the stirrer speed.