Laser Triangulation Topography Principles for Boxboard Surface Evaluation
Laser triangulation delivers uncompressed 3D areal topography data, isolating micro-roughness and void volumes that drive print quality across coated boxboard.
Calender Crush
Surface Calendering
Flat steel rolls mounted in heavy vertical stacks apply high pressure to paper webs during supercalendering operations, and calender crush occurs when excessive nip pressure destroys internal sheet structure. Excessive loading collapses internal voids and crushes cellulosic fibre walls instead of merely smoothing surface asperities. Paper loses caliper, opacity and internal bonding strength rapidly once specific pressure thresholds are exceeded.
Machine operators prevent this defect by monitoring nip temperature and linear load profiles across the web width carefully.
Thickness Loss
Permanent caliper reduction follows severe structural damage inside heavy nip nips. Excessive nip pressure forces fibres into permanent flat configurations without elastic recovery. Converted folding cartons lose stiffness when caliper drops below specification limits during processing.
Packaging engineers measure thickness recovery rates after calendering to detect early signs of fibre crushing.
Surface Porosity
Sheet density increases drastically while air permeability drops toward zero due to total pore closure. Trapped air escapes violently through the sheet, causing localized delamination or blistering under extreme nip loads. Coated papers suffer from binder migration and uneven ink absorption when excessive pressure destroys porous ink-retaining structures.
Laboratory Sheffield smoothness tests confirm that over-calendered paper loses its ability to anchor offset lithographic printing inks properly.