Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The function of a headbox is to deliver a uniform jet of furnish having essentially the same width as the paper web to be produced. The word is derived from earlier days when the hydrostatic head within the box was sufficient to deliver a jet velocity to approximately match the speed of the forming fabric. Except in rare instances, those days are long gone. Rather, the pressure within a modern headbox is maintained by pumps and controls. Air-padded headboxes use an air-space above the furnish as a means of controlling the pressure. Rectifier rolls (or "holey rolls") are cylinders with large holes in them, slowly rotating within an air-padded headbox to help distribute the furnish and prevent deposition of materials. Hydraulic headboxes have neither air spaces nor rectifier rolls. Redistribution of furnish and break-up of flocs is achieved with banks of tubes, expansion areas, and changes of flow direction.
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