A DECREASING-PERMEABILITY MODEL OF WET PRESSING WITH REWETTING

Water removal in wet pressing was modeled by the decreasing-permeabili ty model to represent water forced from a web, with a term added to ac count for water reabsorbed by the web. The model yielded a good fit to data from a pilot paper machine dt low basis weights, where rewet is of greater consequence. Although the model did not give new insight in to the mechanism of rewetting, it did indicate that at low basis weigh ts, water content after a press nip is a linear combination of water t hat hds been expelled from the body of the web under pressure and ''re wet'' water. Also, the model shows that the transition from ''flow-con trolled'' to ''pressure-controlled'' regimes of wet pressing is in rea lity a continuous regime of decreasing permeability in which rewet ass umes increasing relative importance with decreasing basis weight.