Structural Geometry
Planar distortion characterized by angular deviation from a flat reference plane frequently occurs during the drying phase of multi-ply folding boxboard production. Out of plane twist develops when moisture gradients across the caliper create differential shrinkage forces within the cellulose matrix. Rotational curling along diagonal axes prevents proper registration during offset lithography and high speed carton gluing operations.
Converters mitigate this defect by adjusting dryer cylinder temperatures and applying precise water mist to the reverse side of the web.
Moisture Equilibrium
Relative humidity fluctuations in the converting plant exacerbate internal stresses locked inside the paperboard during pressing. Cellulose fibres swell anisotropically upon absorbing ambient vapor, releasing stored mechanical energy through dimensional curling. Storage facilities maintain strict atmospheric controls to prevent the moisture content from drifting outside a four percentage point window.
Cardboard blanks leaving the sheeter with unbalanced moisture profiles warp rapidly when exposed to drier shop floor conditions.
Die Cutting
Flatbed platens require completely planar substrates to achieve clean separation of carton blanks without creating bruised edges or hanging waste. Warped board bridges across the steel rule dies, resulting in incomplete cuts and jammed stripping stations downstream. Mechanical hold down bars on the printing press flatten minor deviations, but severe angular displacement causes jamming at the feeder gate.
Precision optical scanners mounted ahead of the transfer drum reject sheets exceeding maximum allowable flatness tolerances before image application begins.
