Sep 3, 2014
Liner and fluting producers no longer need to make compromises between long felt lifetime and good dewatering. Valmet’s new LineMaster press felt family for liner and FluteMaster press felt family for fluting provide the optimal solution to achieve both.
In the past few years, Valmet’s fabric product development has strongly focused on meeting the requirements set by packaging papers for press felts. As packaging papers are mainly made from recycled fiber, cleanliness issues, plugging and short press felt lifetimes have presented major challenges for producers. Production and energy efficiency also need to be increasingly considered.
Liner and fluting machines have traditionally been run with press felts featuring an open structure. Today, as machine speeds increase, dewatering is carried out both in the nips and through Uhle boxes. The press felts need to be good at both.
“We have now developed press felt families that are specifically optimized for packaging papers: LineMaster and FluteMaster for liner and fluting production,” says Leena Silakoski, Product Manager, Press Felts, PMC, Fabrics business unit of Valmet. “They complement our existing press felt product range, especially for packaging paper machines in the medium speed range. They have, however, also been run on faster packaging paper machines and even on folding boxboard machines with good results.”
Prior to the product launch, the new press felts were thoroughly tested on Valmet’s pilot machine. The first deliveries to liner and fluting machines took place in late 2011. “To date, we have delivered over 100 around the world, and the feedback from the mills has been good. This is also shown by the number of repeat orders we have received,” Silakoski points out.
“A unique feature, and the greatest benefit from both of these new press felts, is the adjustability of void volume thanks to a laminated structure. There can be either two or three layers in the press felt,” explains Ari Tauschi, Product Sales Manager, PMC, Fabrics business unit. “The same basic structure can be easily tailored to each customer’s specific position.”
At the beginning of the press section, where a larger void volume is needed for dewatering, a triple-layer structure presents an ideal solution. A double-layer structure, in turn, is suitable for later press positions where there is less water.
It is also possible to add a so-called volume layer on top of the base structure to further adjust void volume and felt density to remove water either in the nip or through Uhle boxes. The volume layer improves fiber entanglement, increases wear capacity and prevents base fabric marking. The new felts stay open even under high loads in a shoe press or a long-nip press.
Compromising between a long press fabric lifetime and good dewatering has been one of the challenges in making liner and fluting. Achieving a long lifetime has called for open felts and dewatering, mostly over the Uhle boxes. However, in many cases this is not the optimum way to produce paper with regard to dry content, machine runnability and energy consumption in particular. Each machine has its own dewatering strategy, which depends on its speed and construction.
“With the new LineMaster and FluteMaster felt designs, mills do not have to make compromises in felt dewatering at the expense of felt lifetime. Instead, they can optimize water removal by choosing nip dewatering, combined nip and Uhle box dewatering or Uhle box dewatering,” Tauschi says. “Felt lifetime always depends on the mill’s running strategy and preferences. For example, in China the typical lifetimes of LineMaster and FluteMaster press felts have ranged from four to eight weeks.”
Yet another benefit presented by the new press felt designs involves savings and sustainability. As optimized dewatering in the press section reduces steam consumption in the dryer section, a mill saves energy.
“When nip dewatering increases, less Uhle box dewatering and less vacuum are needed. In the best case it may even be possible to close vacuum pumps that consume a lot of energy,” comments Leena Silakoski. “With the new press felts it is possible to optimize the dewatering process on each machine.”
Both LineMaster and FluteMaster press felts are manufactured in Valmet’s modern production facilities at Tampere, Finland.