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A clear vision - Part II

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A clear vision - Part II

February 05, 2012 - 15:16

BRUSSELS, Feb. 6, 2012 (RISI) -Paper machine web inspection and break camera systems play an important role when papermakers are trying to figure out the causes of sheet flaws and associated web breaks. Keeping the cameras and lens clean are just as necessary for detailed images and a clear view of any problems.Read Part I here.

Integrated system

For the first time, the Roermond mill purchased an integrated web inspection (WIS) and web break analysis (WBA) system. "With one system from one supplier the integration is much better," says Stienen. "When you have two separate systems synchronization (of the web inspection cameras at the reel and the upstream web break cameras) is a big issue. In a single system, the cameras talk to each other; it's a tested solution," he concludes.

The web break cameras and the web inspection cameras use the same digital array sensing and the same pulsed LED light sources. With this high-speed pulsing and image capture the fault images are shown without distortion even at high web speeds. When a break or other digital event is detected the system captures and freezes the synchronized images at that exact moment so operators can review the sequence of events which led to a fault or sheet break and determine the root cause. On PM 1, a digital input from the fabric cleaning system shows if problem debris is created, and how effective the cleaning is.

The washing and wiping cycle is scheduled for five minutes at the wet end and 15 minutes at the dry end

The system on PM 1 comprises digital break cameras at the suction pickup, the second press and the size press - on the drive side and on the tending side. A single camera overlooks the pope reel. These cameras and the integrated LED light sources are located in a common housing which incorporates a water spray wash and a wiper blade. All cameras except for the reel camera are equipped with wash and wipe units which use de-ionized water - the same as boiler feed water. The washing cycles are timed at five minutes at the wet end and 15 minutes at the dry end. The washing and wiping works so effectively the cameras have not been touched. One camera at the pickup location on the drive side is in an extremely dirty and constricted location where no operator would want to go. Despite this, the clear cover over the lights and lens remains clean.

One camera at the pickup location on the drive side is in an extremely dirty location where no operator would want to go. Despite this, the clear cover over the lights and lens remains clean

The WIS beam before the pope reel incorporates four cameras which cover the entire web and provide enough resolution to detect the minimum defect size required. The beam can easily be fitted with more cameras if higher resolution is needed in the future. The beam is single-sided with the cameras and the light source adjacent to each other on the top side of the sheet. This reflectance measurement resolves defects in the top layer of the sheet, which is the most important to the mill.

During the commissioning process, the categories of the faults were defined on line by neural-network image analysis software operated remotely by a Metso employee in Finland. This software defines the shape, contrast and textural qualities of a flaw or group of flaws. With the assistance of papermakers common, useful papermaking terms are assigned to these flaw categories. With this service, the customers do not need to learn the details of image analysis, just take part in the definition of common faults. The fault classification library tends to grow with time.

The WIS beam before the pope reel incorporates four cameras which cover the entire web and provide enough resolution to detect the minimum defect size required. The beam is single-sided with the cameras and the light source adjacent to each other on the top side

Weight down, breaks down: remarkable!

For the papermakers, the fault detection capability of the system has been a new-found tool for solving persistent or recurrent problems, the origins of which were unexpected in some cases. Rather than speculation, the diagnosis is based on fact. Frans Jetten, production leader, PM 1 and 2, says, "On the first day we discovered the trim squirts were a problem. We never saw that before. And, before the system, we were convinced that dirt was coming from the dryer section when it was really coming from the radial flow distributor to the headbox." Adjusting the showering sequence in the air pad of the distributor keeps the fiber clumping problem under control.

The integrated system has also improved the learning curve for the operators. "Improvements by the operators take less time and are more effective. That is good to see, since sometimes we had periods with a lot of repeated breaks. It's not the case anymore as problems are solved at the beginning," says Jetten.

Frans Jetten, left, and machine operator Hans van Rosmalen. The integrated system has improved the learning curve for the operators

The reduction in break lost time comes at a time when the basis weights run on the machine are coming down. "Many of the heavier grades have been shifted to PM 3. Now, PM 1 is running lighter weights on the average, but the break lost time has gone down at the same time. That's remarkable!" Jetten interjects.

The quality flaw detection capability is also helping the mill to reduce downstream converting problems and keeping their customers satisfied. The customers are mainly Smurfit Kappa containerboard mills. "Now we know what is being shipped with 100% inspection," says Jetten. The new system allows them to react to developing problems quickly. "If you get rid of minor faults first, you usually don't have a big one," he adds. If problems occur, the recorded faults are stored in the system's database along with reel number so customer complaints can be traced back. The attention to faults has had some positive effects already according to Lap. "The customer complaints have been reduced significantly," he says.