Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The words "velocity 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 velocity forming the angle is relatively shallow, laying the jet gently on the fabric. Velocity forming tends to favor good drainage performance and retention. However, a sheet that emerges from the slice in a flocculated condition will not be improved in formation uniformity by velocity forming. The opposite of velocity forming is pressure forming. 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.
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