Wet Process Drainage — Effects of White Water Chemistry and Forming Wire Structures

This paper reports the effects of white water characteristics and forming wire parameters on wet process drainage. By employing a recently developed lab tester, the present investigation conducted drainage experiments of long (32 mm) fiberglass in polyacrylamide (PAM)-based white water with a real (commercial) forming fabric in position. The forming wires under investigation cover air permeability from 465 to 715 CFM and drainage index from 9.5 to 22. Drainage experiments show that both PAM concentration and shearing (mixing) effect can strongly affect wet process drainage. So, white water of fixed composition, but with a different mixing history may behave very differently, and an increase in input mixing energy usually results in a substantial increase in drainage. Mat basis weight also strongly influences wet process drainage. Although an increase in basis weight always reduces the rate of drainage regardless of wire structure, its impact is much stronger on the wires with a high air permeability and a low drainage index than the ones with a low air permeability and a high drainage index. Another important finding of this study was that drainage index did not predict the performance of a forming wire, and the main causes were believed to be the fundamental differences between the wet-formed glass mat (WFGM) and papermaking processes. Also, correlation between air permeability and wet process drainage was found very complex: while air permeability may be used as an empirical parameter to predict drainage for light weight mats at low PAM concentrations, however, the higher the web basis weight and the higher the PAM concentration, the more likely it would fail.