Valmet’s latest solution for bulk-saving is Aqua cooling calendering. This new patented technology improves the calendering results compared to usual production conditions. With conventional roll nip, the best calendering results are achieved when the web is cool and stiff, like in pilot trials. With Aqua cooling calendering technology, pilot-type conditions are brought to production-level, by cooling down the web before the calendering nip.
Aqua cooling calendering enables production of more lightweight end-product, without compromising functional and visual properties. This will lead to substantial reduction of energy and raw material usage.
Web cooling is enabled by evaporating water from the web with cool dry air blown on both web surfaces. It is possible to boost this effect by spraying a controlled amount of water on the web surfaces just before the evaporation. This cooling will lead to bulk benefit of up to 5%. Thanks to the compact design of this new technology, aqua cooling can be retrofitted to practically any production line.
The dry air is blown on the web with the OptiDry Chill air web cooling units. OptiDry Chill double pass units presented on the left cool the web twice longer than the conventional cooling units on the right. For each 10 °C of lower web temperature, you'll get ~1 %-unit higher bulk!
Thanks to the compact design of the aqua cooling calendering equipment, it is possible to retrofit this bulk saving technology to practically any production line. Aqua cooling technology complements Valmet's bulk-saving calendering offering, which includes the revolutionary metal belt calender as the ultimate lightweighting solution. With aqua cooling technology, it is possible to get almost half of the metal belt calendering benefits with lower investment costs.
Lighter board with better strength properties and lower cost with higher quality: this is the reality for board makers. Stora Enso’s Ingerois Mill in Finland has been improving lightness and bulk for decades. Aqua cooling calendering helped the mill with its light-weighing goal.
Roll cover decisions are complex; the prices, performance characteristics and cover lifetimes vary considerably. Answering these five questions can guide papermakers in making a better choice among today's wide range of roll cover technologies.