18 HEIMBACH
Pulp Paper & Logistics
A quicker way of locating barring problems
New materials and high-frequency analysis are making the source of periodic machine- direction mass variations in paper webs easier to locate. PPL reports
unwelcome irregularities in the paper sheet that are sometimes only visible during end processing. As a rule, such abnormalities are the result of mass variations. More often than not these
B
faults, which can often have expensive repercussions, are only identified in the laboratory because on-machine diagnostic systems are not able to measure with sufficient frequency. Or, to put it more precisely: they are unable to detect MD mass variations in the paper sheet. This is where ODIN comes in – a special measuring fork with a higher scanning frequency. The Heimbach TASK team,
a group of experts who offer diagnostic, measurement and problem-solving services to paper mills around the world, were recently presented with a problem by a customer.
Tracking density This computer-aided visualisation helps to illustrate the core problem in the plan view. In essence, ‘mass variations’ refer to a change in density of the sheet. In this image, which is illustrated in Figure 1, these differences are simplified, with the white areas indicating increased density. In order to gain insights on problems such as this it is
May/June 2018
arring is familiar to most papermakers, but welcomed by no-one. It is the
Figure 1: Increased density in a computer-aided visualisation
invariably necessary to use the ODIN system, as scanners installed on paper machines are usually only able to measure or scan up to a maximum of 100 Hz. In contrast, the measuring fork used with ODIN is capable of scanning up to 3,000 Hz, which opens up many possibilities. The paper machine runs at 1,200 m/ min so the distance between
the periodic mass variations is 150mm.
Values prove facts In the same time that the on-line scanner measures 100 readings, the ODIN scanner measures 3,000. To detect any fluctuation at all, at least 2.1 measurements must be made per barring period which in this case is 150mm – the
difference between the mass variations. A value must therefore be recorded at least every 70mm. The on-line scanning equipment is not able to achieve this, since its scanner only samples at a distance of 200mm. In contrast, ODIN collects data every 6.6mm so it can be regarded as a guarantor of precise measuring (see Figure 2). In a world
Figure 2: ODIN and scanner shown schematically
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 |
Page 37 |
Page 38 |
Page 39 |
Page 40