Environmental conditions are tough because certain areas will have a humidity of near 100% and temperatures reaching 130°C.
In general, paper machines have a total length between 100 and 200 metres and produce paper between 6 and 10 metres wide. Some can produce as much as 2km of paper per minute. In other words, 120km of paper per hour.
The press section and drying section are equipped with hundreds of large roller bearings, each of them critical to the operation of the machine. Because of the criticality of the bearings, vibration monitoring programs using periodic route-based measurements are very common in the paper industry.
Although online monitoring solutions are becoming more common, both hardware and installation costs of these systems often remain an obstacle. As a result, one expects periodic vibration measurements will remain the method of choice in many cases, and for many years to come.
Due to the sheer amount of bearings and the working conditions, monitoring programs will continuously provide for the follow up of the progression of defective bearings, trying to estimate the optimal timing for intervention. For paper plants, it is important to limit the amount of planned maintenance stops to a minimum and certainly to avoid additional unplanned stops for urgent bearing replacements. So, often the maintenance responsible will be very well aware of a severe bearing defect but will want to run until the next scheduled production stop, if unacceptable risks can be avoided.
The following example is a case study where Wi-care™ monitoring system was requested for a defective bearing, to intensively follow up the progression of the defect, allowing to support the decision if it could continue to run through the upcoming weekend, providing a less costly opportunity to replace the bearing.
As always, installation, implementation and commissioning of the Wi-care™ system was completed in less than 15 minutes. Because of the difficult environmental conditions (temperature and humidity), a solution with the high temperature accelerometer with integrated cable and a separate Wi-care™ transmitter was selected. The gateway was installed in the repair shop nearby.
Below is a trend plot of overall vibration amplitude, measured from Friday until Monday (when the machine was stopped).
The amplitudes are increasing slowly and consistently. The blue circle indicates a period of a couple of hours, where production speed was lowered and amplitudes dropped accordingly. The red circle shows a short production stop, because of a paper break, a common event for most paper production machines.
Below plot shows the spectrum of the damaged bearing, with the classic pattern of an inner race defect, with strong presence of running speed sidebands.
Because of the gradual, but certainly not exponentially increasing amplitudes, and by being familiar with the amplitudes that similar bearing defects exhibited in the past, it was decided to continue to run through the weekend. Stopping the machine after the weekend significantly lowered the cost of the repair, while permanently and remotely monitoring the defect made this possible without taking unacceptable risks.
Included are two pictures illustrating the severely damaged bearing, encountered during the repair. Also, the 3D waterfall graph comparing the vibration spectra before and after the repair.