Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The function of hydrofoils ("foils" for short) is to aid in removal of water from a wet web in the early stages of dewatering. On a Fourdrinier paper machine the foils are placed under the forming fabric. Their shape is designed to create suction as the foil and wet web pass over the surface. Hydrofoils also create a brief pressure pulse as the fabric passes over the leading edge. The alternating pressure and vacuum of a series of hydrofoils tends to move fibers around in the wet web, slightly improving the drainage and uniformity of the resulting paper. Also, the pulsation tends to change the drainage mechanism from pure filtration to a combination of filtration and thickening. The washing action of hydrofoils tends to remove fiber fines and fillers from the wire side(s) of a paper sheet. Another function of the hydrofoil is to doctor water from the under-side of the forming fabric.
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