This Wi-care™ success story deals with a drying cylinder bearing defect, encountered in a paper machine.
In general, paper machines have a total length between 100 and 200 meters and produce paper between 6 and 10 meters wide. Some can produce as much as 2000 meters of paper per minute. In other words, 120 kilometers of paper per hour.
The press section and drying section are equipped with easily hundreds of large roller bearings, each of them critical to the operation of the machine. Environmental conditions are tough because certain areas will have a humidity of almost 100% and temperatures reaching 130°C. Because of the criticality of the bearings, vibration monitoring programs using periodic route based measurements are very common in paper industry.
Although online monitoring solutions or 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 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 I-care™ was requested to install a Wi-care™ monitoring system on 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 done in less than 30 minutes. Because of the difficult environmental conditions (temperature and humidity) a solution with high temperature accelerometer with integrated cable and a separate Wi-care™ transmitter was selected. The gateway was installed in the repair shop nearby.
Below trend plot shows the overall vibration amplitude, measured from Friday till Monday (when the machine was stopped).
Some comments to this graph. It can be seen that the ampliudes are constantly, but rather slowly increasing in amplitude. The blue arrow indicates a period of a couple of hours, where production speed was lowered and amplitudes dropped accordingly. The red arrow shows a short production stop as a result of paper break, a fairly 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.