Board Distortion
Asymmetrical fiber alignment across paperboard plies causes opposing corners of flat sheets to lift in opposite vertical directions. Complex sheet deformation where diagonal corners curl away from the neutral plane is recognized as diagonal twist warp. Internal strain differentials between top and bottom linerboards trigger angular sheet twisting when environmental humidity shifts.
Machine direction fiber orientation that strays from the true mechanical axis of the paper machine induces torsional shear across the sheet. Moisture absorption expands fibers across their diameter rather than along their length, converting angular fiber misalignment into rotational forces. The defect classification applies to sheeted paperboard and corrugated board structures, ceasing to apply to continuous web rolls under tension.
Fiber Orientation
Jet-to-wire speed ratios on headboxes determine the dominant angle of fiber alignment relative to machine direction. Angular offset between grain directions in outer plies creates balanced shear stress during drying cycles. Non-parallel fiber orientation across multi-ply webs forces adjacent layers to expand along competing diagonal axes when relative humidity changes.
Converting Impact
Twisted sheets cause continuous feeding failures on high-speed feeder tables by catching against side guides and registration stops. Automated carton blanks cut from twisted board warp out of square during folding and gluing operations. High-speed packaging machinery drops overall efficiency when feeding stock exhibits diagonal lift exceeding six millimeters from flat inspection tables.
Pallet conditioning under controlled atmospheric conditions reduces moisture gradients that aggravate sheet twisting prior to die cutting.
