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.
Jet Wire Speed Ratio
Kinematic Ratio
Paper machine headbox stock exit velocity compared directly against forming fabric speed defines the initial shear environment during wet web formation. Calculating jet wire speed ratio establishes whether pulp slurry lands on the moving wire faster or slower than fabric speed. This operational setting governs fiber orientation, tensile anisotropy, and Z-direction sheet structure on paper machines.
Structural Effect
Operating at a jet wire speed ratio different from unity creates shear stress within suspended fibers that aligns cellulose elements along the machine direction. Dragging the jet by running slower than the wire stretches the suspension, whereas rushing the jet creates micro-turbulence that alters fiber distribution. Matching jet speed exactly to wire speed minimizes fluid shear, producing a more isotropic fiber orientation with square tensile strength properties.
Converting operations require square sheets for uniform box stiffness, whereas high speed printing presses benefit from higher machine direction tensile orientation. Machine operators manipulate headbox slice pressure to fine-tune this velocity relationship during production changes.
Operating Boundary
Mechanical drive limits and headbox pressure capabilities restrict operational adjustments during high speed paperboard manufacturing. Velocity control cannot compensate for severe stock consistency fluctuations or improper headbox dilution settings across the machine width. Drainage forces on the forming table lock fiber orientation rapidly, rendering subsequent velocity adjustments ineffective once initial dewatering occurs.
Operational control applies exclusively to the wet forming zone prior to mechanical vacuum dewatering.