Belt Calendering: A New Concept for Sheet Property Enhancement, 1999 Papermakers Conference Proceedings

Paul Nahass, Karen Crawford

Parameters which influence calendering results include nip length, contact surface hardness, temperature, and dynamic nip pressure. Use of a belt in the calender nip significantly enhances printability of paper and board sheets while bending stiffness and bulk are preserved or improved. This is accomplished by extending the calender nip, allowing for longer, more uniform contact. Calender belts have been supplied by Albany International and are performing successfully in pilot and commercial-scale operations, with good runnability and belt lifetimes. Economic benefits observed include raw materials savings and higher quality printed surfaces.

Belts have been supplied with various hardness values, typically 86 ShA, 91 ShA, or 80 ShC. Belt constructions can be incompressible or compliant, affecting nip width and dynamic nip pressure in some configurations. Machine configurations include a modified shoe-press concept or multi-roll nip. Some belt construction possibilities could allow for relatively simple rebuilds of existing calenders.

Comparisons have been made between belt calendering and both conventional and soft nip calendering. Printability has been tested and correlates well with calendering process parameters from these configurations. Printability also correlates well with surface microsmoothness (Ra) of the sheet, which can be measured efficiently with commercially available instruments.