By Mark Williamson, journalist engineer, Thornhill, ON, Canada
Paper machine web inspection and break camera systems have played an important role by providing that visibility with detailed, synchronized images of sheet flaws and break events. When the cameras and lights are clean, everything is fine. But how long does that sharp image of the web last in a dirty, splash-filled papermaking environment, especially at the wet end where many faults and breaks start? It seems not very long, in many cases. If too frequent operator cleaning of the camera lens and light source is required, the entire system can fall into a state of disrepair and machine operators will forget about it out of frustration or indifference.
Fewer breaks, well defined causes
This gradual or sometimes rapid deterioration of image quality is a concern of many papermakers, including the staff at the Smurfit Kappa Roermond Papier mill in the Netherlands. The mill staff decided to equip PM 1 with an integrated web inspection and web break analysis system. Keeping the web cameras and light sources continuously clean with no operator intervention was at the top of the list of system requirements. The 4,950-mm trim machine produces testliner with medium grammages.
Wouter Lap, manager of operations, says, "You can have the best system, but if the images are not clear, it is of no use." By installing a Metso Process and Quality Vision ( Metso PQV) system with automatic washing of the camera lens and light source cover plate, the mill's objectives have been met completely. The image quality has been sustained, and the return on investment is better than expected after the startup in February 2011.
Lap says, "We saw a significant decrease in the total number of breaks. Comparing a period of 10 months before installation with the period 10 months after installation of the system, we saw a reduction of 37% in the total number of breaks. It is not fair to assign this result only to the camera system. However, I am convinced that a significant part can be assigned to the indirect help of the WIS/WBA system. We would not have reached the same result without the cameras."
The system has helped them to define unknown problems better. "In the period before installation, approximately 26% of the total number of breaks was judged for reasons unknown. After installation, this number has almost been halved to 14%. Also, the reliability of the judgment (break reason) is much better," he adds.
Maintaining image quality
As part of the mill's supplier evaluation process a Metso process camera housing with integrated wash and wipe equipment was tried out on PM 3, which has an existing camera system. One original system camera was installed in the Metso PQV enclosure. Bart Stienen, process control engineer, reports, "We didn't see any image deterioration. And, it was a very dirty, difficult location." Adding to that proof, a previous-generation PQV reference from a sister Smurfit Kappa mill in Germany confirmed that cleanliness and image quality was maintained without operator intervention. Furthermore, mill staff agreed that using water for washing is a lot cheaper than compressed air used in other designs.
Good image quality was also ensured by the selection of digital cameras in the PQV system. The digitized image signals are not subject to electrical interference and image distortion possible with analog cameras.
To be continued ...
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