20 HEIMBACH


Speed measurements at the headbox


and Know-How) department: Whether they are investigating one or in some cases all sections of a paper machine, offering advice on machine technology or performing analyses – no two jobs are alike. What TASK team does know for


C


sure, however, is that on many occasions a customer needs facts first so they can pursue a line of enquiry and can help with specific measurement technology. In this particular case they were in action during the start-up phase of a machine producing folding boxboard and carried out measurements on three headboxes in order to assess the jet-wire ratio. The customer had ordered the


complete clothing package from Heimbach and it was asking TASK to check the jet-wire speed.


Measurements are complex There are often jobs in which speed measurements results helped to determine the cause of increased fabric wear and/ or disproportionately increased sheet breaks. Other jobs consist of precision-tuning drive systems or synchronising transfer positions.


In addition to this TASK


frequently checks machine settings, such as speed indicators, for accuracy – and this was also relevant for this particular assignment.


March/April 2017 Figure 1: Fabric speed in the filler as well as surface and back layers


Facts for forming Once on site, the Heimbach engineers exchanged views with the production manager who suspected that the three fabrics were not running at exactly the same speed, which could lead to displacement or movement of the sheet layers during couching. It wasn’t at all clear, furthermore, whether jet speeds were displayed correctly in the control room, which for machine operators in the forming section is the control instrument per se: after all, you need correct information that you can rely on. Perfectly calibrated and correctly displayed jet speeds – also called ‘jet-wire ratio’ – are the basis for being able to manipulate the formation and some of the stability characteristics of the end product.


First results The measurements began and the jet speeds as well as those of the forming fabrics of the filler,


back, and surface layers were identified. The first significant result was: All three fabrics were running at exactly the same speed (Figure 1), so that TASK was able to quickly reassure the production manager with regard to his first concern. The speed displayed in the


control room also corresponded to the result of the measurements. However, in the back layer a major difference of jet speed was discovered: The measured speed was around 35 m/min below the value that was shown in the control room. For the first time it was suspected that the problem might be down to a calculation error and/or incorrect programming of the speed indicator.


Ratio - the decisive factor Next, together with the paper makers on site, the Heimbach employees dealt with the speed differentials between jet and fabric, i.e. the ‘ratio’. You can


appreciate how fundamentally important the provision of the correct value is in this context; after all, fibre orientation and formation are set according to this. Even though the back layer appeared to have a ratio of 10m/ min, the measurement that was taken showed 25m/min (Figure 2). In this circumstance, the paper makers quite logically assumed that the jet was 10 m/min faster than the fabric and therefore more fibres were aligned in a cross direction. In fact, the jet was actually 25 m/min slower than the fabric and therefore the fibre orientation tended more to the machine direction. TASK therefore increased the jet speed until a real ratio of zero m/min was achieved.


Slice opening and jet speed After this had been accomplished the slice opening of the headbox was changed to find out whether the jet speed remained constant.


hange is the order of the day in Heimbach’s TASK (Technical Assistance, Service


Pulp Paper & Logistics


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36