Pulp Paper & LogisticsPulp Paper & Logistics


INDUSTRY NEWS 15 VALMET


machine speeds with the same or better paper properties, such as higher elongation and low porosity. The dewatering speed through


the felt in the Z direction in the nip is key to maximized dewatering in the nip. Optimized dewatering in the


first and second nips provides a base for good runnability. For example, maximum nip dewatering downwards in the first nip gives a low draw level because the bottom side of the sheet is drier. Good dewatering in the first nip and the optimum water content in the felt also reduce edge-related problems. The felt designs and nip performance can be optimized either by changing both felt positions (PU and the first press) to more dense and/or lighter felts, or by changing only one of them. Even felt change increases hydraulic pressure and improves dewatering on both sides.


A unique base structure “SprintMaster has a unique structure, with a base fabric consisting of two woven bases with a special sublayer on the paper side. This optimizes water removal and start-up, maintains high felt strength and extends its lifetime,” Silakoski explains. The absorbent sub-layer


densifies the felt structure in the middle, enabling the felt to immediately reach high saturation and stay saturated throughout its lifetime. Hydraulic pressure increases in the nip, resulting in a fast start-up and excellent nip dewatering. According to Silakoski,


rewetting is minimal. High hydraulic pressure pushes water through the felt quickly, and the special sublayer element blocks


Figure 3: SprintMaster’s optimized base fabric consists of two woven bases with a special sublayer on the paper side


the water inside the felt so that the surface of the felt does not get too wet. The base structure does not


burst like nonwoven or hybrid felts sometimes do, even under high wear. The woven base structure and high CMD yarn


density give very good CMD stability. The base structure of SprintMaster offers an optional


Case studies for three SprintMaster high-speed machines


Case 1: Press section: conventional 3 nips plus 4th press/paper grade: SC/PU press felt: SprintMaster • Fast start-up, very good nip dewatering • Good water capacity in the first and second presses→ less water to the third press • No edge issues, good runnability, about 10% lower draw • SprintMaster now used as the standard felt with a 100% market share


Case 2: Press section: conventional 3 nips and a 4th press/paper grade: newsprint/PU press felt: SprintMaster • Fast start-up, very good nip dewatering • No edge issues, good runnability • SprintMaster now used a the standard felt with a 100 per cent market share


Case 3: Press section: conventional 3 nips/paper grade: testliner/first press felt: SprintMaster • Very fast start-up, very good nip dewatering • 20 per cent higher nip dewatering in the first press • High energy-saving potential • Good runnability, fewer breaks • SprintMaster is the new standard felt with about a 75 per cent market share


More information from Leena Silakoski, product manager at Valmet. Email: leena.silakoski@valmet.com Tel. 358 40 774 9855.


May/June 2015


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