Structural Alignment
Physical alignment parameters dictate the spatial distribution of cellulose fibers within a paperboard web during wet-end sheet formation. Fiber orientation describes the angular distribution of fibers relative to the machine direction, establishing the anisotropic physical properties of the paperboard. Machine speed, headbox jet-to-wire speed ratio, and shake mechanics govern this structural layout.
Hydrodynamics Distribution
Stock delivery from the headbox slice deposits dilute fiber suspension onto the moving papermaking wire. Fiber orientation shifts toward the machine direction when jet velocity differs from wire speed. Aligning fibers predominantly in the machine direction increases tensile stiffness along the web length while reducing tear strength across the sheet.
Balancing jet-to-wire ratios produces a more isotropic sheet with predictable folding performance in both principal axes. Automated ultrasonic and optical transmission sensors measure orientation angles continuously across the web width. Papermakers adjust headbox recirculating flows to correct diagonal grain alignment that causes finished carton twisting.
Anisotropy Limit
Orientation metrics quantify directional physical properties in machine-made paperboard sheets. Fiber orientation analysis does not apply to synthetic nonwoven webs or wet-laid random hand sheets. Structural evaluation ends after fiber networks undergo complete fiber collapse during high-pressure wet pressing.
Measurement accuracy drops in multi-ply board grades with opposing layer orientations.
