Measurement Variance
Thickness fluctuations across a paperboard web arise when internal moisture gradients or mechanical pressures shift during production. Board caliper drift identifies the incremental increase or decrease in substrate thickness occurring along the cross-machine direction or throughout a long manufacturing run. Stability in board caliper drift ensures consistent package performance during high speed cartoning where minor variations disrupt vacuum feed or folder gluer performance.
Production Mechanism
Calendering rolls exert high pressure to compress fibre mats into uniform sheets but nonuniform wear or thermal expansion across those rolls creates localized thickness deviations. Operators monitor this through continuous scanning gauges that track deviations against target specifications. If the moisture profile enters the nip too wet, the fibre undergoes excessive crushing, which induces permanent density changes that appear as board caliper drift downstream.
Corrective actions involve adjusting individual shower zones or altering crown profiles on the finishing equipment to restore uniform compression.
Operating Tolerance
Printing presses and converting lines require predictable substrates to maintain register and adhesive application integrity. Excessive drift forces adjustments to plate settings or folder glue pressures that slow down output capacity. Standard tolerances permit minor variance but exceed limits when the board loses structural uniformity at the creasing station.
Reliable board caliper drift control governs the difference between a high volume production success and a rejected lot.
