R. J. N. Helmer, G. H. Covey, W. D. Raverty and N. Vanderhoek
The formation potential of two short fibre pulps, a bleached Tropical Hardwood Kraft (THK), and a bleached Eucalypt Kraft, (BEK), were investigated. Sheets were formed at various consistencies and velocities consistent with commercial operation on the UoM former. The sheets formed during the study were assessed by standard commercial tests which included an ultrasonic test for anisotropy and a beta-ray formation test. The flow conditions were found to be very important for optimising the forming potential of a given pulp. Both of the pulps investigated exhibited an optimum formation, but at different process conditions. The results suggested that an optimum flow condition exists for obtaining the best formation from a given pulp. The BEK pulp was found to have a superior forming potential. These results may be extrapolated to suggest target, idealised flow conditions for forming paper on commercial papermachines. Furthermore, a tool has been developed by which the performance of pulps under machine conditions may be predicted with more confidence in the laboratory.
Analysis of the forming potential of many pulp stocks has largely been restricted to sheets formed using a standard handsheet former, one of a number of assorted laboratory formers, or through expensive pilot scale trials. Standard handsheet and conventional laboratory forming devices generally have forming conditions which are far removed from the commercial process (1-16). None of these devices has been deemed to be a truly satisfactory predictor of what may be expected on a commercial machine from a given fibre stock. Hence, predicting the performance of new furnishes at commercial process conditions has been difficult. The production of paper in the laboratory where controlled forming conditions result in an anisotropic sheet of predictable properties, which match those of papers made on a commercial paper machines, has been a long desired instrument for many researchers.
The University of Melbourne laboratory former (UoM) produces an anisotropic sheet of paper with repeatable properties (17). Controlled forming conditions result in laboratory sheets with properties which match those properties of papers made on commercial paper machines at similar operating conditions (same consistency with an equivalent jet to wire velocity, depth and vacuum profile). The laboratory sheet former simulates commercial processes by employing a novel interpretation of the flow in the forming region resulting in a system where stock flows over a stationary wire, (with a free upper surface).