Hydrodynamic smoothing in the sheet forming process

We present a series of experiments performed to evaluate a family of stochastic models designed to detect and quantify any cooperative hydrodynamic effects during a paper forming process. The smoothing parameter, s, ranges from O for no correlation between successive layers to 1 for the case of perfect infilling of earlier voids. For laboratory handsheets formed over a range of grammages and crowding numbers, we find s to be positive in all cases, confirming that the smoothing phenomenon exists. Hand-sheets formed at crowding numbers close to 1 exhibit variability, at the 1 mm scale, decaying from over 10 times random at 4 g m^-2 to approximately random above 50 g m^-2. We conclude that substantial hydrodynamic smoothing does occur though it is insufficient to overcome the opposing effect of flocculation.