A headbox is provided which provides an improved uniformity in the velocity profile of the stock solution across the slice opening. As a result, improved fiber alignment is provided across the width of the entire slice opening and mis-alignment of the fibers towards the outer edges of the slice opening is avoided. The headbox includes an improved nozzle design with pondsides that are not parallel to one another but which are angled inwardly as they extend from the tube bank to the slice opening. Further, several columns of outer tubes of the tube bank may also be angled inwardly as they extend from the header to the nozzle section. The center tubes would be disposed in a parallel relationship to one another. A sealing arrangement is provided between the roof of the nozzle section and the pondside which permits the incorporation of a double knuckle for extending and retracting the roof to adjust the L/b ratio. In an alternative embodiment, the roof includes a rectangular extraction which is retracted and extended by a double knuckle and which needs no special sealing arrangement between the extension and the pondsides.

An arrangement for feeding stock to a headbox in a papermaking machine which comprises at least one stock header with an inlet for receiving stock into the header and a plurality of stock header outlets permitting stock to leave the header. For each stock header outlet there is a stock conduit downstream of the stock header outlet permitting stock to pass from the stock header outlet, through the conduit to the inlet of the headbox. The arrangement includes a dilution header for feeding a diluent such as water to a plurality of stock conduits. The dilution header has an inlet for receiving a diluent not the dilution header and a plurality of outlets permitting the diluent to leave the dilution header. For each dilution header outlet, there is a diluent conduit permitting the passage of a diluent from the dilution header into a stock conduit. According to the invention, the diluent is fed into a stock conduit at a location immediately downstream of a stock header outlet and the stock header together with the stock header outlets is designated such that the velocity of the stock flowing through the stock header is substantially equal to the velocity of the stock in an upstream end of the stock conduits.

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, thus increasing CD strength of the manufactured sheet. Vortex forming means are described for a plurality of tubular elements in the diffuser box for generating controlled axial vortices in the machine direction 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. Further embodiments, which include methods and apparatus for generating vorticity by pressure pulse devices and magnetically actuated finned bodies, are also described.

In a paper machine headbox, a stock suspension flow passes through turbulence pipes (14a.sub.n) and is distributed into superimposed layers. Stepped expansion spots (16) of the flow cross-section area of the turbulence pipes (14) or the positions of trailing elements starting from between the pipe rows (R.sub.n) and extending to the slice duct (12) of the headbox control the onset and level of turbulence in each layer. Turbulence is generated in different phases of the flow in different layers by arranging the expansion spots (16) and/or the trailing elements in superimposed layers to be located at different distances from the slice opening (13) of the headbox, whereby a different turbulence prevails at the slice opening (13) in different layers of the stock suspension flow.

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, thus increasing CD strength of the manufactured sheet. Vortex forming means are disclosed for a plurality of tubular elements in the diffuser box for generating controlled axial vortices in the machine direction 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.