Methods And Apparatus To Enhance Paper And Board Forming Qualities

Abstract

Methods and apparatus to enhance paper and board forming qualities with insert tubes and/or a diffuser block in the paper forming machine headbox component which generates vorticity in the machine direction (MD) which is superimposed on the streamwise flow to generate a swirling or helical flow through the tubes of the diffuser block. Tubes of the diffuser block are designed such that the direction of the swirl or fluid rotation of the paper fiber stock may be controlled and the direction thereof is controlled in such a way to provide effective mixing, coalescence and merging of the jets of fluid emanating from the tubes into the converging section, i.e., nozzle chamber of the headbox. Also disclosed is the effective mixing of the jets generating cross-machine direction (CD) shear between the rows of jets that form at the outlet of the tubes inside the nozzle chamber of the headbox to align paper fibers in the cross-machine direction. In another alternate embodiment, the generation one or more counter-rotating vortex pairs (CVPs) may be set up inside each tube instead of a single vortex per tube. The counter-rotating vortices inside the tubes result in more effective interaction of the jets once leaving the tubes. The CVPs may be generated in four orientations in the tube block, generating controlled axial vortices promoting mixing of the jets of paper stock from the tubular elements as the jets flow into the nozzle chamber to a uniform flow field of stock at the slice opening for the rectangular jet.