Alignment Fluctuation
Variations in paper properties along the direction of the paper machine’s movement affect the runnability of the substrate. This machine direction variance is caused by fluctuations in stock flow, headbox pressure, or drier temperatures during paperboard production. Minimizing this variation is critical to ensuring that the paperboard behaves consistently during printing and converting.
Tensile Difference
Physical properties such as tensile strength and stiffness are always higher in the machine direction than in the cross direction. This anisotropy is created as the fibres align themselves with the flow of the slurry on the forming wire. When the variance along this axis is high, it causes unpredictable feeding on folder-gluers and presses, because the paperboard may stretch or warp unevenly as it moves through the tension zones.
In extreme cases, these variations can lead to web breaks on rotary presses, necessitating immediate line stops and causing substantial waste of both ink and substrate.
Process Stability
Controlling the stock delivery system is the primary method for reducing fluctuation in the paperboard web. Modern headboxes use automated feedback loops to adjust the slurry flow in real-time, which stabilizes the fibre orientation. This automated control ensures that the finished roll has uniform stiffness from start to finish.
