Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The words "pressure forming" refer to the angle at which the jet of furnish from a headbox slice impinges upon the forming fabric near to a breast roll or forming board. In the case of pressure forming the angle is relatively steep, driving the jet toward the fabric. Pressure forming tends to set a mat of fibers against the surface of the forming fabric very quickly, possibly "sealing the sheet" (impeding further drainage). Pressure forming is sometimes used to achieve a desired sheet structure or break up fiber flocs. The opposite of pressure forming is "velocity forming," in which the jet is laid almost parallel onto the forming fabric. Velocity forming tends to favor good drainage performance and retention.
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