20 HEIMBACH Edges in focus
Seemingly small defects on the edges of a paper web can have huge effects further on. Heimbach TASK specialists have been investigating the reasons. PPL reports
dryer cylinders that are under pressure, the mills themselves are too, so the last thing manufacturers need now is costly disruptions to production and loss of quality. Edge problems in the pick- up position are a persistently annoying issue. The specialists from Heimbach TASK are very familiar with this, having similar experiences time and again around the world: Even small adjustments can eliminate gremlins in the long-term.
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Effects on the whole process The causes of complications in production are as diverse as the different grades of paper. One of the reasons why customers often seek help is the occurrence of edge problems. One common edge issue occurs when the paper web, or the trimmed edge of the sheet, begins to be carried along with the pick-up felt. As soon as this defect moves into the press rolls, all subsequent groups or sections are prone to sheet breaks. It’s a classic situation: the trim from the fabric or parts of it follow the pick- up felt. The sheet edge remains stuck to the central press roll and tags along or breaks. This results in edge damage, edge creasing or folding of the edge.
Sensitive pick-up position Minor cause, major impact – this ubiquitous saying applies equally
July/August 2020
aper production stopped being taken for granted a long time ago. It is not only the
Pulp Paper & Logistics
Press configuration Tri-Nip with steam box
to edge problems. This chain reaction occurs mostly in context with the pick-up position. When
troubleshooting, the attention of TASK is initially focused on this position and the related clothing.
They find that in most cases the surface of the felt is dirty, or even fused, and therefore smooth. The smoother the felt surface, the more the sheet tends to adhere to, and then run with it (glass plate effect). How is it possible for the
pick-up felt to change so much? The causes would tend to be incorrectly adjusted suction elements, inadequate suction box design and too high temperatures due to a steam box. Let’s take a closer look at these weak points in the following cases.
Figure 1: Suction couch roll with optimum width adjustment of the suction zone
Correct setting of the suction elements Encountering edge problems after only two days of operation, the
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