b'DRYER SECTION INNOVATIONSTHICKER HARD METAL COATING WITH FINERThicker metal coating with finer particles prevents corrosionPARTICLES PREVENTS CORROSIONVoith has a TerraDry Express coating for all dryer cylinder applications.improved TerraDry C, CT, CN and CS arebondingapplied thermally through a HVOF (High Velocity Oxygen Fuel) process. The pressurised gas mixture flow accelerates through a nozzle at high speeds that lead to very dense particles with excellent bonding properties. The aim is to achieve a hard metal surface with the highest possible protectionpoor bondingagainst corrosion. The temptation for some suppliers is to use large particleless corrosionhigh corrosion sizes, for example 75 microns. Voithresistance resistanceuses small particle sizes, for example 45 microns, which create a denserFigure 4. Fine particles with small spaces decrease the risk of corrosion and improve bonding.structure and higher bonding strength, as shown in Figure 4. This does take a little longer to build up the coating thickness, but the payback is a higherunbalanced heat distribution andFurthermore, not only are the rolls resistance to corrosion.ultimately to uneven drying of themore durable after metalizing by paper web with a corresponding lossVoith, the service life of doctor blades FEWER WEB BREAKS THANKS TOof paper quality. Furthermore, anhas also been extended by up to 100 HOMOGENEOUS TEFLON LAYERS irregular coating of Teflon can result inpercent.The function (uppermost) layer candifferent curing times across the length certainly improve the performance ofof the cylinder during its application. IfCONCLUSIONthe metalized coating; for example,not thoroughly cured, the Teflon will beUltimately, the paper manufacturer it can be formulated to improveeasily removed in localised areas. needs to produce tons of paper. This contaminant resistance and/or surfacecan only be done efficiently when durability. The temptation for someEIGHT YEARS IN OPERATION the paper machine is running. Voith service suppliers is to rush the metalOther paper manufacturers haveOn-Site Dryer Services is often called coating and then make up for it withbenefited from the detailed work ofon to replace coatings applied bynot only the Teflon function layer. Voith On-SiteVoiths On-Site Dryer Services. At theother service providers who haveare the Dryer Services experts know that a thinIndonesian paper manufacturer PTclearly tried to speed up the job.rolls more function layer improves heat transfer,Tjiwi Kimia, the team applied TerraDryIn the long term, the high qualitydurable after leading to more efficient drying of theCT Express coatings to two rolls on itsof Voith TerraDry Express cylindermetalizing, paper web. The higher heat transferNo. 11 machine in January 2010. Thiscoatings and, most importantly, thethe service can increase dryness, reduce sheetcontributed to a longer service life andattention to detail from the Voithlife of doctor breaks and improve sheet quality. running time of the dryer cylinders.On-Site Dryer Services teams moreblades has Despite a running time of more thanthan makes up for the investmentalso been A homogeneous application of the10 years, both rolls continue to workwith longer component life, higherextended by Teflon coating is a prerequisite.so well, that no reconditioning haspaper quality and a reduction inup to 100 An irregular coating leads to anbeen necessary. web breaks.percent.88 WORLD PULP&PAPER'