Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
Papermakers use the word "forming" to describe the process in which a slurry of fibers having a solids level of 0.3 to 1% is converted into a wet web having a solids level of about 15 to 22%. Forming is accomplished with a variety of equipment. The most traditional equipment is the single-fabric Fourdrinier paper machine. On a Fourdrinier machine a wide jet of dilute furnish is applied from a headbox onto the surface of a continuously moving wire screen. Water is removed by gravity and with the help of hydrofoils (or alternatively, table-rolls), vacuum boxes, and vacuum applied at the couch roll. A dandy roll (screen cylinder) or a top-wire may be used to make the sheet more uniform. Twin-wire machines (gap formers) employ two continuously moving fabrics and the jet of furnish is directed into the closing gap. This format tends to produce a sheet that is symmetrical in the z-direction.
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