Zhejiang Forest United Paper’s PM 6: Pioneering OptiDry Coat double-pass air drying technology

Zhejiang Forest United Paper successfully started up its PM 6 board machine in February 2025. The company invested in a new machine to plug a gap in their production capacity. “Before the PM 6 start-up, we had already achieved a closed-loop industry chain across the upstream, midstream, and downstream packaging production – except for coated white lined chipboard. PM 6 fills this capacity gap,” says Tong Lin General Manager of Zhejiang Forest United Paper.

PM 6 produces coated white lined chipboard grades, ranging from low basis weights (230–240 g/m²) to medium-high basis weights (340–390 g/m²). Product types include gray-back white lined chipboard, kraftliner, and coated kraftliner. The board machine features the world’s first OptiDry Coat double-pass, which combines three advanced air drying technologies in a single compact solution.  

Tong Lin, General Manager of Zhejiang Forest United Paper  

Compactness, efficiency, and quality with new air drying technology

PM 6 uses multiple OptiDry Coat coating air dryers to dry three top coating layers and one back layer, all of which are applied using OptiCoat Roll coating heads. Zhejiang Forest United Paper is pioneering the OptiDry Coat double-pass for drying the starch which is used on the back. Any initial concerns about adopting the new technology were quickly overcome, as the company has been very pleased with the results. They have found the biggest benefits include high drying efficiency and quality control, easier tail threading and operation, and a shorter machine length due to a short coating loop.

“The paper web runs through very smoothly, and drying performance is excellent. The narrow spacing significantly shortens the length of the board machine, improves tail threading efficiency, and reduces civil construction costs,” Xiaobin Chen, Deputy Production Director at Zhejiang Forest United Paper confirms.

Xiaobin Chen, Deputy General Manager of Zhejiang Forest United Paper

Excellent quality without curling

The OptiDry Coat double-pass features three dryers in one. First, the high-intensity air dryer section quickly removes free water. Next, the turning dryer section turns the web without contact at a lower temperature. Finally, the moisture control section stabilizes moisture and temperature at high air speed or heat.

The implementation of the OptiDry Coat double-pass system for back drying has directly addressed common challenges related to the curling of the board. “This system’s implementation has resulted in significant improvements in both curling and flatness, and customer feedback has been really positive,” Xiaobin Chen says.

The OptiDry Coat double-pass air dryer has three dryers in one.

Worry-free operation with automation

Operators have found the Machine Control System (MCS) very user-friendly. It automatically adjusts the gap between the web and dryer based on coating and moisture changes. “It’s basically foolproof and very easy to use. The MCS takes care of everything automatically, making it worry-free,” Leiming Shou, Production Manager, Zhejiang Forest United Paper says. “It automatically adjusts the positive and negative pressure to control the paper web and keeps the gap between the web and dryer consistent, which ensures the web stays very stable.”

Leiming Shou, Production Manager of Zhejiang Forest Paper

OptiFlo headboxes ensure high quality

In addition to coating and drying technology, Zhejiang Forest United Paper has been especially happy with the four OptiFlo Foudrinier headboxes Valmet supplied.

“Currently, our surface smoothness reaches 300–400 s, and coated paper smoothness is controlled within 1.0 µm. We also ensure excellent printability. Whether it’s offset, rotary, or digital inkjet printing, our paper delivers consistently outstanding print results,” says Xiaobin Chen. “This achievement is underpinned by the key role of Valmet’s headboxes in sheet formation, allowing the base paper’s 2-sigma cross-direction basis weight to reach 0.36 g/m² in optimal conditions. This guarantees uniformity, a stable aspect ratio, and high consistency, ensuring print uniformity and laying a solid foundation for subsequent coating and printing processes."  

Changzheng Yang, Project Manager at Zhejiang Forest United Paper and Jibao Hui, Senior Product Sales Manager at Valmet

Close and prompt cooperation

Zhejiang Forest United Paper has been very happy with the cooperation with Valmet. “From supply to installation and commissioning, everything was timely, and any issue was resolved efficiently,” says Changzheng Yang, Project Manager at Zhejiang Forest United Paper. “I would rate our cooperation with Valmet a perfect 10! The service is prompt and considerate – they really stand in the customer’s shoes,” adds Tong Lin.

Arto Koski, Senior Paper Technology Manager at Valmet, Leiming Shou, Production Manager at Zhejiang Forest United Paper, Jibao Hui, Senior Product Sales Manager at Valmet, and Jinming Fan, PM 6 Production Supervisor at Zhejiang Forest United Paper.