Pulp Paper & Logistics


HEIMBACH 21


customer was rightly surprised. Regardless of who supplied the felt, every time a new one was installed, the sheet followed the felt and folded in the press. A series of investigations enabled


light to be cast on the subject. The TASK team examined the dry content of the trim, the edge deckles of all suction chambers in the forming and press sections as well as the steam blow box. Measurements of the moisture content of the individual sections were followed by felt permeability analysis. This involves injecting pressurised water into the felt and measuring the flow rate. All the checks, investigations and analyses led to the following diagnosis – the edge deckles of the suction chambers in the suction couch roll and suction press roll were not in the optimum position. This resulted in low dryer content at the sheet edges and subsequent following of the trim. In addition there was unequal load distribution of the first press on FS/DS.


These findings and the


recommendations for optimisation enabled fast and precise


corrections of all relevant settings. The machine has been running without problems ever since. The general advice is that for


optimum suction at the sheet edges, suction box deckles should be set to about 5-10mm outside the paper sheet and permanently aligned with the sheet width. In order to protect the fabric edges from excessive wear, the suction box deckles should be slightly offset against each other in the forming section (as shown in Figure 1).


Targeting the steam box The next case concerned a high- speed paper machine. In the case of fast running machines, steam boxes are often used to increase production or to correct profiles. However, operators frequently complain about edge problems, an issue that in most cases leads to the need for an early removal of the pick-up felt. There is no doubt that an


increase of sheet temperature results in improved dewatering, but this is often achieved at the expense of the pick-up felt. The escaping hot steam is pulled into


Figure 3: Temperature peaks around the edge zone, with the infrared image above the temperature measurements


the felt by the suction press roll. The felt edges heat up and the fusion of the surface that was


referred earlier occurs. Such thermoplastic change of the material is often increased further when a steam box is too wide and/or suction press roll deckles are set too wide. All of these problems had occurred in this case. The analyses by Heimbach TASK showed that the width settings of the discharge and suction zones were not ideal. Movable edge deckles at the steam box as well as an optimum setting of the edge deckles at the suction press roll can remedy the situation (Figure 2). The infrared images showed temperature peaks of up to 10 deg C higher in the critical edge area (Figure 3). As in the first example just a


Figure 2: Suction press roll with optimum width adjustment of the suction zone and optimum adjustment of the steam box


few simple steps were enough to eliminate the causes of the production problems.


July/August 2020


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