Runnability problems, sheet picking, and dusting caused by poor dryer cylinder release are challenges troubling many paper mills. Dirty dryer cylinder surfaces that reduce drying capacity and lead to sheet moisture profile deviations are also often encountered. The solution to problems like these is Valmet's* dryer Roll Cover DOH (earlier known as DryOnyx H) release coating for doctored drying and cooling cylinders. It continues the good work of DryOnyx Z and DryOnyx ZL – with improved features.
The supporting base layer is now a highly wear resistant new-generation carbide coating, which provides superior durability compared to its predecessors. Quadrupled wear resistance extends the lifetime of the coating significantly and reduces recoating costs as there is no need to build up a completely new supporting layer.
The highlight of this new coating is its release layer, made of a unique fluoropolymer exclusive to Valmet. It has been optimized for excellent release and doctoring properties, as well as stable operation due to its good resistance to wear and flaking.
Valmet Dryer Roll Cover DOH is designed for efficient onsite application. The benefits of onsite coating application include reduced shutdown time and low cylinder temperatures, made possible by a special release polymer that cures under powerful UV light. Time-consuming cylinder heating is no longer needed, and such adverse effects of heating as cylinder deformation, balancing changes and head sealing damage can be completely avoided.
Valmet Dryer Roll Cover DOH has very low surface energy, which results in improved release and cleanliness. This innovative polymer also maintains its hardness at high dryer cylinder operating temperatures, which means less wear and longer coating lifetimes.
Another major benefit is the coating's good doctorability. Thanks to special additives used in the new release polymer matrix, its friction coefficient is 80% lower than that of previous coating versions. The resulting benefits include more stable doctoring, less heat build-up at the tip of the doctor blade, a better cleaning result, longer coating and doctor blade lifetimes, as well as lower drive power consumption.
In addition to Valmet Dryer Roll Cover DOH, Valmet also offers Lead Roll Cover GO-W coating for doctored dryer section lead rolls and paper guide rolls. It works especially well in positions after sizing and coating stations and improves their cleanliness.
( *Metso (Paper) until Dec. 31, 2013)