Machine Direction Fiber Orientation Mechanics in Packaging Board
Jet-to-wire velocity ratios govern machine-direction fiber orientation, setting board anisotropy ratios that dictate box compression and score crack resistance.
Creasing Depth
Impression Geometry
Penetration of a male creasing rule into paperboard against a female matrix channel creates a controlled line of mechanical weakening along prospective fold hinges. In packaging converting, creasing depth defines the vertical distance the rule tip travels below the undisturbed board surface during impression formation. DIN 55437 specifies test methods for evaluating crease parameters on solid board and folding boxboard.
Precision tools measure this indentation relative to total caliper to verify that inner plies delaminate without fracturing outer liner coatings. Correct penetration depth forces the middle board layers to shear along natural fibre planes, forming an internal hinge structure that lowers bending moment during carton erection.
Matrix Alignment
Matching rule width and matrix channel width to sheet thickness ensures uniform shear force distribution across the scoring line. When creasing depth remains too shallow, the board retains high bending resistance, which causes panel bowing and glue line spring-back during automated folder-gluer operations. Excess depth drives the creasing rule excessively into the sheet, cracking top print coatings and severing surface fibres.
Packaging converters adjust die-cutter platen pressure to maintain depth within five micrometres across the entire cutting plate area.
Rupture Boundary
Target values fail when converting recycled paperboard grades containing short secondary fibres that lack tensile elongation. Insufficient fibre length prevents internal ply separation, causing the back liner to split even under light creasing depth settings.