Pulp Paper & LogisticsPulp Paper & Logistics
INDUSTRY NEWS 15XERIUM 15
(as in Figure 2) and the special duplex version Huyspeed BD with its very fine top surface, Xerium has developed a design concept to accomplish the market requirements. By providing increased drainage at a lower caliper, the third design of the product family, Huyspeed BE performs with top results on high performance tissue machines. As a result, Huyspeed is now considered a benchmark on tissue machines especially using waste paper and intensive high pressure needle shower. Due to its increased drainage,
Huyspeed BE enables not only reduced cleaning effort but also to reduced pressure with high pressure needle showers. On balance this leads to valuable savings in water consumption. Beyond that the gentle mode of operation delivers improved felt lifecycles. The major advantage of
Huyspeed BE is its wide operation window. This makes it an attractive option for tissue machines operating across a wide grade range.
Venting opportunities on tissue machines • Traditional venting in tissue operation The applications being considered here are the suction pressure roll and pressure roll positions. Roll covers for these positions are designed to generate the proper nip intensity at the maximum load. Traditionally, these covers are specified in the 30 to 45 P&J range since bulk and conformity to the Yankee are key design criteria. Cover compounds must possess good abrasion resistance, crack resistance and hardness stability (to prevent hardening from operating against the hot Yankee dryer).
Figure 2: One of the Huyspeed range – GU 1+1 laminates version
Historically, the use of venting on these applications was limited by a number of variables. In suction pressure roll positions, venting consisted of suction-through holes only. The through-hole diameter is limited by the hole diameter in the shell so the total open area typically ranges from 16 to 19 per cent. Adding blind drilled holes to the suction pressure roll was not often used. In order to fit blind drilled holes in the suction pattern, relatively small and ineffective holes would be required (0.078-in or 0.085-in diameter). Blind drilled holes would also require the felt to take on more moisture. This is not desired when the suction pressure roll is followed by a pressure roll position, or if the felt conditioning system is not capable of handling the additional moisture. The use of grooves was restricted
due to the fact that soft covers will deform under pressure. The groove height is reduced and the walls will bulge inward under pressure. The narrowing of the groove will restrict the flow of water resulting in the remaining void volume becoming ineffective. The narrowing of the grooves also creates the possibility of pinching the felt in the nip. Common industry guidelines only utilized grooves on roll covers harder than 12 P&J. At 40 P&J, studies have shown that the void volume contributed by the grooves is one
half of the initial available void volume.
• Improved technology Advancements in roll cover and press felt technology have opened the door to increase the utilization of venting in tissue applications. Softer polyurethane covers possessing higher modulus materials offer greater abrasion resistance, better hardness stability and stable hysteretic characteristics. These stable physical properties of the polyurethane covers now make it possible to utilize newer venting patterns to allow increased nip dewatering and decreased energy consumption. Slightly harder 20-30 P&J polyurethane covers develop similar nip intensities as 30 to 45 P&J rubber covers. Advancements in rubber
compounds have also generated more opportunity to utilize venting in softer covers. Superior abrasion resistance combined with low hysteretic characteristics allows 30 to 45 P&J rubber covers to run longer. Rubber covers possess greater chemical resistance and stronger bond strength. The softer material offers optimum conformity to the Yankee surface for improved sheet qualities and drying. The advancements in polyurethane cover materials now make it possible for grooves to withstand the conditions in the
suction pressure roll nip. Adding grooves to a suction pressure roll can improve the nip dewatering in the press. The grooves increase the open area and available void volume in the cover. Void volume generated by grooves is also assisted by vacuum since the grooves intersect the suction through holes. Increased nip dewatering will generate both a drier sheet and felt exiting the nip. The drier sheet requires less external energy to completely dry the sheet and the drier felt now can offer additional void volume in the second press (pressure roll nip). Xerium has greatly improved rubber cover technology in recent years. New rubber covers can also utilize grooves in suction pressure roll applications. With this engineered grooving technology, ‘EnerVent’, soft rubber covers can also offer increased nip dewatering. The EnerVent grooves are geometrically incapable of closing. These grooves have greater wall stability and are less affected by groove narrowing in the nip. The result is more effective void volume and greater nip dewatering. The soft rubber covers still maintain excellent bonding strength, chemical resistance and conformity to the Yankee surface. Case studies have documented 10 plus per cent increases in production and substantial reduction in energy usage, including 41 per cent reduction in fuel usage to the hood. More information from Robert
Marchhart at email: robert.
marchhart@xerium-europe.com * Oliver Baumann is Global
VP Technology, PMC/IT, Robert Marchhart Global Product Manager, PMC/Engineered Fabrics and Glen A Harvey is Director of Rolls Engineering Technology NA at Xerium
July/August 2014
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