Pulp Paper & Logistics


VOITH 23 Smooth operators


Attention to detail in the grinding and metalising of dryer cylinders is one speciality of Voith’s On-site Dryer Services. PPL reports


Q


uality problems and web breaks in paper production are often the result of


inadequate roll coatings in the dryer section. When recoating existing cylinders, Voith’s On-Site Dryer Services attach great importance to ensuring a homogeneous surface. In the long term, thorough preparation and attention to detail by an experienced team pays off for paper manufacturers through reduced wear, improved paper quality and higher productivity. Various practical examples


show that the work of Voith’s service teams makes it possible to significantly extend the runtimes of components.


Longer runtimes reduce life cycle costs Downtime on paper machines is always associated with costs and as such is kept as short as


possible. The metalising and grinding of dryer cylinders is a high investment item for the paper manufacturer. It requires downtime and if not done correctly can be very expensive in terms of further downtime and lost production. There are too many cases in the paper industry where service suppliers cut corners, resulting in further unnecessary lost production for the papermaker. Voith shows how attention to


detail on each process step when metalising a dryer cylinder can provide long-term payback for the paper manufacturer.


Careful grinding reduces vibrations The temptation can often be to grind off the cylinder surface quickly to save time, for example, in steps of 0.04 mm by using high grinding pressures. Voith’s experience proves that a gradual removal of thinner layers, for


Figure 2: Grinding steps to remove problem areas on the cylinder surface


example 0.02 mm, reduces the risk of vibration, producing a more homogeneous cylinder surface. The subsequent blasting process removes all grease residues. This ensures that the new coating bonds better to the surface. “Like most things in life, time


spent to prepare the foundation pays off when building subsequent processes,” says Carl Taylor, global product manager of the dryer section and on-site service at Voith. “For example, time spent preparing the cylinder removes any evidence of chatter marks and ensures optimum particle bonding of the coating.” A case of unwanted chatter marks caused by too coarse grinding is shown in Figure 1.


Grinding is often required to


remove damage or corrosion in the cylinder surface. It is critical to ensure the


Figure 1: Chatter marks on a dryer cylinder caused by uneven grinding


problem area is removed before metalising the cylinder. Figure


2 shows how corrosion should be removed through grinding. If grinding is stopped too soon and some evidence of corrosion remains, this will not be apparent once metalised but will show through at a later stage. Voith ensures that all problem areas are fully removed before metalising the cylinder, resulting in a longer service life.


Significant increase in production possible Just how important this precise procedure is can be seen in the example of PT Indah Kiat Perawang, an Indonesian paper manufacturer. In August 2017, the company chose a service provider to metalise dryer cylinders on its PM6 machine. After only nine months, the drying cylinders showed severe surface wear and corrosion, as seen in Figure 3. The result: a drop in paper quality and an increase in number of


4 January/February 2020


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