18 HEIMBACH On the trail of moisture
Thermographic measurements using imagery and data are able to identify where too much moisture remains as the edge of a paper web. It’s a process used by Heimbach’s TASK team. PPL reports
discover what is tried and tested. Just think for a moment about travel and the scenes in airports and at train stations on the news. One detail is shown again and again: the thermal imaging camera. This tool has been around
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for many years, but in the current situation is of particular importance. This is mainly due to the fact that a thermographic camera measures at lightning speed and without contact. Heimbach’s TASK team is not fighting a pandemic, of course, but uses thermography to investigate moisture problems in the paper web.
Fault analysis during operation If the edge area of the sheet is suddenly too wet, those responsible quickly start to sweat.
One of Heimbach’s TASK team carries out a thermographic measure on a paper making line
This is because the origins are usually difficult to identify. So how can you locate the reason and eliminate the cause without incurring major production losses? To overcome this difficult challenge Heimbach uses thermographic measurements to record temperatures without contact and to display the results visually. The heat differences that can be determined provide reliable information concerning
the point at which moisture content deviates from target. For this, of course, not only the
right equipment is needed, which consists of an infra-red camera and special software. What is needed above all is qualified personnel to analyse and interpret the recorded data using extensive application experience and technical know-how.
How does thermography work? Thermography is a non-contact measurement procedure. With this method, the camera measures the infra-red radiation emitted by an object, for example the paper web or the dryer fabric. These recordings reflect the temperatures that are transferred from the drying cylinder to the paper web. The temperature differences
The thermographic camera measures the infra-red radiation emitted by an object and displays it as an image
September/October 2020
must be taken from either the sheet or the dryer fabric, as dryer cylinders are smooth and highly reflective. Thermographic measurement is unable to provide
he coronavirus pandemic has certainly taught us a lot, but has also allowed us to re-
meaningful results when applied to surfaces that reflect more strongly than they emit. In the case of dryer cylinders then, surface temperature would have to be determined by contact thermometers. It is also difficult for thermal imaging cameras to measure in the forming and press sections, due to difficulties in detecting high and low temperatures prior to the first dryer cylinder as fibres and water still have the same temperatures at this point. You could say then, that the thermographic camera only becomes really ‘hot’ in the dryer section. In turn, the software makes it possible to display thermal deviations clearly and in colour.
A practical example Heimbach’s TASK team measures temperature differences across the paper web on site and can thus detect moisture differences in the width of the sheet. It can be said, in principle, that the higher the temperature difference, the greater the moisture difference at the measured point. A customer complained of wet
edges on the drive side of his paper machine. The resultant problems were more frequent sheet breaks and potential production losses. Internally the problem was suspected to lie in the dryer section. Before a thermographic measurement can be taken, the steam box must be turned off 24 hours beforehand: otherwise, the
Pulp Paper & Logistics
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