Evaluating Machine Direction Anisotropy and Crease Ratios in SBS Board
Evaluating machine direction anisotropy and crease depth ratios in SBS board balances fold integrity against corner springback on high-speed cartoning lines.
Fiber Orientation Hydrodynamics
Fluid Physics
Headbox stock suspension flow generates fluid shear forces that align wood fibers along primary velocity gradients during web formation on paper machine wires. Understanding fiber orientation hydrodynamics allows paper mill operators to influence fiber alignment before vacuum dewatering fixes web geometry. This fluid motion dictates machine direction physical properties across paper and paperboard substrates.
Anisotropy Control
Continuous adjustments to jet velocity and wire speed govern how fiber orientation hydrodynamics affects structural squareness across manufactured paperboard grades. Shear fields formed within the slice nozzle orient individual cellulose fibers parallel to stock delivery streams. Changing slice geometry or headbox pressure alters local turbulence profiles, modifying fiber alignment before wet web consolidation.
High shear rates align fibers predominantly in the machine direction, increasing tensile strength while reducing cross direction tear resistance. Balanced fluid shear yields isotropic sheet properties necessary for high speed converting and uniform score folding performance.
Quality Limit
Physical testing of finished board rolls exposes non-uniform tensile properties when shear stresses fluctuate across the wet end forming area. Edge effect turbulence generates local alignment deviations along web margins, creating dimensional instability during subsequent printing operations. Dewatering elements freeze fiber arrangements rapidly, stopping structural rearrangement before slurry reaches uniform density.
Fiber orientation hydrodynamics operates strictly within the wet forming zone prior to initial press nip mechanical dewatering.