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Pulp Paper & Logistics


HEIMBACH 21


occasionally be a cause. Referring back to this study, the ‘133.33 Hz problem’ was still present at the forming table – focusing attention on to the upstream process. It was necessary then to consider the stock approach of the machine, for which the same applies as before: If an irregularity is present here already this can still sometimes be preserved all the way to the reel. In some instances, the paper machine itself can actually be helpful, as several inconsistencies that could be responsible for barring may even be ‘ironed out’ on the machine. This term is fitting – during the course of their activities, Heimbach TASK personnel often discover that machine parts are able to offset a large part of the barring that occurs.


This did not, however, apply


to the case in question, and the investigation continued. How, then, to find the fault? Quite simply testing was moved on to the stock approach unit just behind the last classic measuring position, where a


positive result was obtained, which brought the pressure screens into focus. Here, where the screens transport the stock through the pulsation dampeners to the headbox, we found a frequency of 33.33 Hz. The source of fault was identified. Why? Because the screen has a rotor with four blades, and four times 33.33 comes to 133.33 (see Photo 2).


Clarity for all involved There was wear in this component – quite normal once its standard lifetime had been reached and possibly exceeded. The result of this advanced wear was higher pressure fluctuations, which the dampener was no longer able to cushion sufficiently. The screen was therefore also responsible for the barring seen in the finished sheet. With the cause now revealed,


maintenance personnel could check and repair blades, basket, blade distances and slot widths as necessary. Combining the application of a process of elimination with the ODIN


measuring equipment had provided the solution to the problem.


Fast facts ODIN was in fact specifically developed for such applications. The measuring fork is constructed from high-strength carbon and weighs only two kilos – making it a true ‘lightweight’ capable of accomplishing heavy-weight work. Previously heavy metal


devices were used, resulting in backbreaking work. Today, fortunately, everything is high tech, which applies not only to the measuring fork but also other items that form part of the ODIN package. Data is transmitted with a measuring amplifier to a telemetry system, and recorded wirelessly by a laptop (see Photo 3). The high performance software of the computer then performs a Fast Fourier Transform (FFT) and breaks the time signal of the measurement down into individual frequencies makes the


facts available. A complete ODIN measurement including evaluation usually takes a day, though in this particular complex case machine took longer.


Forward-looking actions More often than not patience is required before certainty can be established, but the benefits of mass variation measurements extend beyond the detection of the sources of barring problems. ODIN can also be successfully employed for preventive maintenance. Damage to units or machine components can be detected and verified before barring actually occurs, with subsequent prevention of production losses. Through this kind of regular maintenance paper quality is kept at a consistently high level. Once faults have been located, paper technologists have access to important – and valid – information allowing them to plan repair stoppages in the most efficient way.


Photo 3: The ODIN measuring device May/June 2018


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