Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The function of a pressure screen in a paper machine thin-stock recirculation system is to remove shives (fiber bundles) and other large, hard contaminants from the furnish. Conventional pressure screens use baskets with either slots or holes to admit the fibrous "accepts" flow and reject the contaminants. Slotted screens usually have a sculptured pattern that helps fibers to become aligned and pass through the screen. Pressure screens are equipped with various types of rotors to continuously redisperse any fibers that start to accumulate on the screen surface. Because fibers can pass through a slotted screen individually, but not as fiber flocs, papermakers sometimes choose to add retention aids ahead of pressure screens in order to achieve a favorable balance of formation uniformity and adequate retention of fine particles.
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