The hydrodynamics of formation improvement by blades in twin-wire formers

A mechanistic model of formation improvement in paper caused by blades in twin-wire formers has been developed. Hydrodynamic stresses and strains have been linked to strain of fibre flocs and the consequent displacement of fibres relative to,forming fabrics. The model takes into account the unique conditions in typical gaps, namely the smallness of the gap size relative to fibre length, consistency gradient in the z direction, fibre type, and machine conditions such as fabric tension, speed and angle of wrap. Estimates from the analysis are shown to be consistent with experimental observations.