Lighter board with better strength properties and lower cost with higher quality: this is the reality for board makers. The market is demanding somewhat contradictory properties from the produced boards. 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.
The folding boxboard product brand Tambrite by Stora Enso has always met the needs of the market. Tambrite’s long history means it has also been the one creating the requirements, since it was among the first to focus on lightweighting. Valmet’s new aqua cooling calendering is another step towards making Tambrite even lighter.
Tambrite’s story is fascinating. The main goal set 30 years ago remains the same. First it was about being profitable and a pioneer; later it was about sustainability and meeting the needs of the market. Lightness was – and remains – the primary feature when Stora Enso Ingerois develops its Tambrite folding boxboard products.
Never settling for just maintaining the status quo, Ingerois is continuously looking for ways to improve Tambrite. This time, the focus was on the board-making process. The mill wanted to substitute the Yankee process and Yankee cylinder with a process less restrictive on productivity and speed. The decision was made to find a new bulk-saving calendering process and bypass the Yankee cylinder.
Sometimes the answer lies right in front of you, but finding the means to get there is the tricky part. “We have pilot facilities at Järvenpää to test calendering. We knew that pilot calendering always delivered better bulk than normal, mill-scale production: the cooler the web, the better the bulk,” says Development Manager Mika Viljanmaa from Valmet. It took a while before the idea really struck: cooling the web with water and cool air.
After process modeling by Senior Development Engineer Jari Ilomäki and a few pilot runs, Viljanmaa decided to share the idea with Antti Veitola, Production Manager at Ingerois, and Product Development Engineer Erja Nevanperä. The board machine maker needed cooperation of a board producer.
After some more calculations and pilot runs, it took only a little time to convince the Stora Enso personnel that the new process was working. “The results of the pilot trials were convincing. There was a clear correlation between the web temperature and bulk,” explains Veitola. “As a final check, we ran a number of different pilot trials to compare the effects,” he continues. After being assured, it was just a matter of making things as fast as possible.
The first ever aqua cooling calendering system was installed at the Ingerois mill in the fall of 2015. There were some minor challenges related to the newly developed equipment. “In research and development projects, there are always some issues that cannot be predicted. However, all the problems were fixed,” explains Viljanmaa. “Big companies like Stora Enso and Valmet may face extra challenges because R&D projects are integrated into the model of a normal project, and sometimes this is not the ideal way to operate. But with people working together, things work very well,” Veitola says.
“We talk about bulk-saving potential instead of precise numbers. We are happy with the clear results. The results basically depend on how much cooler the web can be in these kinds of process conditions,” Veitola explains.
With the improved lightness and stiffness properties of Tambrite folding boxboard, it is good to go forward.