Deformation Metric
Structural evaluation of folding boxboard requires a measurement of the localized force applied during the scoring process. This deformation, termed creasing strain, describes the ratio of material displacement to the original thickness of the board along the crease line. Precise control of this parameter prevents the rupturing of the outer liner during subsequent high-speed folding operations.
The measurement helps packaging converters adjust the depth of the creasing rule to match the specific caliper of the board. This calculation relies on the relationship between the groove width and the board thickness, ensuring the board bends along the planned axis without splitting.
Material Response
Fibre separation and internal delamination occur under the scoring tool to create a clean hinge. When creasing strain is applied correctly, the double-wall board experiences controlled shear stress that does not penetrate the surface. Adjusting the board moisture content is necessary because dry fibres become brittle and fracture easily.
The folding torque must decrease without compromising the structural stiffness of the finished carton.
Process Failure
Cracked creases on the outer face of a package represent a total failure of the barrier coating. Excessive creasing strain ruptures polymer layers and exposes raw pulp to moisture or oil. This breakdown of the barrier allows humidity to penetrate the board and soften the box during transport.
High-speed cartoning lines experience jams when fold resistance varies.
