Predicting Set off Migration in Stacked Packaging Board under Non Uniform Compression
Predicting set-off migration requires calculating local pressure peaks across board caliper variations to set safe pile heights and barrier coat weights.
Non Uniform Compression
Strain Distribution
Localized pressure variation across web surfaces creates uneven mechanical compaction of cellulose fiber structures during calendering or converting operations. Density fluctuations in paperboard base sheets cause differential resistance under nip pressure, yielding uneven thickness reduction across the sheet width. Structural failure from non uniform compression alters localized ink absorption, bending stiffness, and surface smoothness parameters.
Hard spots within fiber webs absorb disproportionate force, causing localized fiber damage while adjacent low density zones remain uncompacted. Process control systems attempt to equalize nip pressures across the machine width to maintain consistent mechanical response.
Caliper Loss
Variations in base sheet grammage generate non uniform resistance as the paperboard web passes between rigid calender rolls. High basis weight zones experience extreme localized compaction, crushing hollow lumens and degrading sheet thickness, while lower weight areas receive minimal calendering pressure. Experiencing non uniform compression across the web profile creates permanent caliper variations that compromise structural performance during package converting.
Lost caliper directly reduces creasing resistance and box compression strength in finished corrugated containers. Uneven thickness reduction causes web steering errors on high speed printing lines, leading to register misalignments and web breaks. Adjusting zone controlled crown rolls mitigates localized pressure spikes along the contact line.
Print Defects
Inconsistent surface compaction alters liquid absorption rates, producing mottle defects in offset and flexographic printing applications. Systematically measuring non uniform compression pinpoints calender roll wear and web formation irregularities before commercial converting runs.