Creasing Rule Selection for Coated Folding Boxboard Conversion
Selecting steel creasing rules and matrix channels for coated FBB requires matching board caliper and CTMP core shear limits to prevent surface cracking.
Bending Stiffness Reduction
Crease Yield
Packaging board testing measures the loss of flexural rigidity that occurs when a creasing matrix compresses folding boxboard along a score line. This physical weakening, known as bending stiffness reduction, allows paperboard to fold cleanly into cartons without tearing the outer linerboard. The value expresses the ratio between the moment required to bend an uncreased board sample and the moment required to bend a creased sample of identical width.
Standard creasing rules press fibrous webs to break internal hydrogen bonds along designated fold channels, creating a localized hinge. Lower resistance at the crease prevents bowing across carton panels during high-speed gluer operations. The metric ceases to apply when board structures fracture entirely or when creasing tools cut through surface fibers.
Score Mechanism
Mechanical deformation during scoring forces middle fiber layers to delaminate into thin parallel sheets. Controlled delamination determines the magnitude of bending stiffness reduction achieved during converting. Depth of penetration by the creasing rule alters internal shear stresses within multi-ply board.
Deep rule penetration creates wider internal delamination zones, dropping bending resistance and easing panel squareness. Excessive penetration destroys liner integrity, leading to score cracks on printed folds.
Line Tolerance
Automatic packaging lines require uniform resistance along every fold to prevent jam events in feeding hoppers. Deviations in bending stiffness reduction alter the force required by folding swords on side-seam gluers. Board batches showing insufficient stiffness drop buckle under axial thrust during top-loading carton fill operations.
High stiffness retention leads to bulging carton walls that distort display geometry on retail shelves. Plant operators adjust male rule width relative to female channel depth to hold crease resistance within ten percent of target specification.