Optimizing coated paper operations through high-temperature supercalendering

Optimizing the coated paper finishing process offers many benefits to papermakers, including increased throughput, reduction of off-specification product, as well as more efficient calendering and converting operations. Even more importantly, optimized finishing allows mills to improve the printability of their product to become more competitive in existing and new markets. Supercalendering at higher steel roll surface temperatures is one optimization technique that has been proven useful to either increase throughput or to attain a new glass grade level. This paper will discuss high-temperature supercalendering trials held in cooperation with several major European high-quality coated paper producers. These trials were undertaken by the papermakers as a result of their positive experience with high-temperature soft-nip calenders. One goal of the trials was to examine the possibility of controlling the gloss profile. The ability to control glass profiles will give the supercalender operator a tool for levelling the typical frown profile to ensure uniform gloss for every roll of paper across the entire reel. To achieve the scape of the trials, profiling external induction heating was used to increase and to control the roll surface temperature at 75 mm (3 inch) spacing. This paper will summarize the results achieved and the predicted benefits for the coated supercalender operation. In addition, this paper will discuss the process control techniques required to coordinate a full-size system including on-line measurements, control actuators and algorithms.