On-Line Multinip Calender

The direction in calendering is towards on-line solutions, even with such higher value-added printingpapers as SC-grades and glossy coated papers.Soft calendering has enhanced the finishing of several grades, enabling quality which is better than with conventional machine calendering in hard nips, while at the same time simlifying the process by reducing the number of nips needed and employing simpler web runs. Still, there are limitations to soft calendering. Smoothness improvement is limited by relatively low nip pressures due to the wider nips associated with the large-diameter rolls used, and by the limited number of nips. On the other hand, off line supercalenders have continued to produce the highest quality capability. The biggest drawbacks to conventional supercalendering are the relatively slow speed, off-line operation and dependence on the use of filled rolls. These factors limit the production capacity and prevent supercalenders from meeting the challenge presented by faster paper machines.While advances in hot soft calendering and supercalendering have improved the state of calendering technology, there is a clear need for a new approach to calendering to produce SC-type grade, coated printing papers and similar value-added grades. That approach is OptiLoad.OptiLoad incorporates many innovative developments, such as Dura polymer-cover soft rolls and heated intermediate rolls. The top and bottom rolls are softcovered, zone-controlled Sym-Z rolls or multizone Sym CD rolls for effective caliper profiling. The OptiLoad principle makes it possible to fully relieve the total weight of each intermediate roll, utilizing lever arms and hydraulic relieving cylinders. Till now 18 off-line and 6 on-line OptiLoads including near future start-ups have already been sold in the world.