Piezoelectric Sensor Frequency Response Calibration for Folding Boxboard Converting
Piezoelectric sensor frequency response calibration prevents amplitude distortion during high speed creasing by matching amplifier cutoff to rule strike transients.
Pre-Load Relaxation
Force Decay
Viscoelastic behavior in cellulose fibers causes a gradual reduction in the resisting force of paperboard under a constant compressive deformation. The phenomenon of pre-load relaxation is a critical factor when stacking filled corrugated shipping cases in warehouses. When a box is subjected to a constant stacking load, the internal stresses in the paperboard decrease over time.
This force reduction can lead to unexpected box failure even if the initial load was well below the board’s rated ultimate strength.
Stack Stability
Long-term storage of heavy packages puts continuous stress on the bottom boxes of a pallet. This load triggers pre-load relaxation as the wood pulp fibers slowly rearrange their molecular structures to relieve the internal tension. As the fibers relax, the vertical walls of the corrugated box lose their rigidity and begin to bow outward.
This deformation reduces the box’s top-to-bottom compression resistance, increasing the risk of the stack leaning or collapsing. The rate of this load decay accelerates in high-humidity environments where moisture weakens the hydrogen bonds between the cellulose fibers. Packaging designers must account for this decline when calculating safety factors for shipping cartons.
Structural Assessment
Laboratory testing of paperboard creep and recovery helps predict long-term performance. Measuring pre-load relaxation allows engineers to specify board grades that resist structural failure over extended storage periods.