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24 VOITH


Pulp Paper & Logistics


web breaks. In August 2015 and July 2017, Voith’s On-Site Dryer Services team applied TerraDry C Express coatings to six rolls on the PM3 machine. In 2018, the team inspected the paper machine to find that the Teflon coating was still in near mint condition. This had a significant impact on paper production. “The customer had recorded significantly fewer paper breaks, and the paper quality had increased,” says Taylor.


Thicker hard metal coating with finer particles prevents corrosion Voith has a TerraDry Express coating for all dryer cylinder applications. TerraDry C, CT, CN and CS are applied 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 protection against corrosion. The temptation for some suppliers is to use large particle sizes, for example 75 microns. Voith uses small particle sizes, for example 45 microns, which create a denser structure and higher bonding strength. This


January/February 2020


Figure 3 (clockwise from above): The surface of the dryer cylinders on IK Perawang’s PM6 showed severe wear and corrosion before Voith applied its On- Site Dryer Service


does take a little longer to build up the coating thickness, but the payback is a higher resistance to corrosion.


Fewer web breaks thanks to homogeneous Teflon layers The functional (uppermost) layer can certainly improve the performance of the metalised coating: for example, it can be formulated to improve contaminant resistance and/or surface durability. The temptation for some service suppliers is to rush the metal coating and then make up for it with the Teflon function layer. “Our Voith On-Site Dryer


Services experts know that a thin function layer improves heat transfer, leading to more efficient drying of the paper web,” explains Taylor. “The higher heat transfer can increase dryness, reduce sheet breaks and improve sheet quality.” A homogeneous application of the Teflon coating is a prerequisite. An irregular coating leads to an unbalanced heat distribution and ultimately to


uneven drying of the paper web with a corresponding loss of paper quality. Furthermore, an irregular coating of Teflon can result in different curing times across the length of the cylinder during its application. If not thoroughly cured, the Teflon will be easily removed in localised areas.


Eight years in operation Other paper manufacturers have benefited from the detailed work of Voith’s On-Site Dryer Services. At another Indonesian paper manufacturer, PT Tjiwi Kimia, the team applied TerraDry CT Express coatings to two rolls on its PM11 machine in January 2010. This contributed to a longer service life and running time of the dryer cylinders. Despite a running time of more than 10 years, both rolls continue to work so well, that no reconditioning has been


necessary. Furthermore, not only are the


rolls more durable after metalising by Voith; the service life of doctor blades has also extended by up to 100 percent. Ultimately, the paper manufacturer needs to produce tons of paper. This can only be done efficiently when the paper machine is running. Voith On-Site Dryer Services is often called on to replace coatings applied by other service providers who have clearly tried to speed up the job. In the long term, the high quality


of Voith TerraDry Express cylinder coatings and, most importantly, the attention to detail from the Voith On-Site Dryer Services teams more than makes up for the investment with longer component life, higher paper quality and a reduction in web breaks.


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