Caliper Variation Reduction and Fiber Savings from Improved Calender Roll Tolerances, TAPPICon25

Minimizing caliper variation in the paper sheet is critical for optimizing product quality and profitability. As product sheet caliper consistency is directly impacted by calender roll tolerances, roll geometries must be examined when pursuing caliper variation improvement. The goal of this 2.5-year study was to determine how caliper variation could be reduced by tightening calender roll tolerances.

In this work, we examine a paper sheet produced on a coated board machine. Initially, quality data were analyzed from paper made with calender rolls ground to the machine’s conventional tolerances. Halfway through the study, these calender stack rolls were replaced by rolls ground for improved profile, journal concentricity to roll face, and roundness. Two distinct grades of coated board were examined. Both were determined to have significantly reduced caliper variation (26.8% and 16.1%) attributable to the improved roll geometries. In addition to discussing the effect to caliper cross-direction variation when calender rolls with precision-ground tolerances are installed, in this study we will share opportunities for improved strength and fiber savings as a result of this increased control.

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