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Monitoring vibration is one of the most effective predictive maintenance tools, particularly in the paper and pulp industry, where mills are constantly searching for ways to increase productivity. Vibration analysis can potentially benefit most rotating machines since all machinery has a degree of vibration due to the difficulty of balancing moving parts. It can be used to measure quickly, easily and non-invasively. One of the most common causes of failure is bearing degradation in gear drives. There is no visual inspection that can detect this problem before it causes such a failure. Vibration analysis provides an easy and cost effective way to trend the wear on the internal bearing, allowing maintenance engineers to schedule essential repair work without any loss of production.
There are a wide variety of sensors and systems to choose from dependent on many factors including installation requirements, budgetary limits etc. Piezoelectric accelerometers tend to be the preferred type of sensors for most vibration monitoring in the paper industry as they have been proven to be both highly reliable and versatile. The industrial piezoelectric accelerometers perform well over a wide temperature and frequency range and are unaffected by dirt, oil and most chemical atmospheres.
One of many paper mills that has benefited from installing vibration monitoring equipment from Monitran Ltd as part of their predictive maintenance schedules produces in excess of 250,000 tonnes per annum of fluting and liner paper for the packaging industry.
Here, more than 450 of Monitran’s MTN/1100 series vibration sensors have been installed, hardwired to 30 MTN/3000 switch boxes throughout the plant. These sensors were chosen as they use the industry standard two-wire constant current method of transmission, are ideal for use in on-line and off-line systems and directly compatible with most commercially available data collectors. A monitoring programme is instigated on a five weekly cycle, with the resultant data being used to identify maintenance requirements for planned shutdowns.
The planned maintenance routine at the mill is an integral part of a proactive risk management and safety policy operated by the company, that has seen it invest in the region of £150 thousand over the last 3 years in new monitoring systems and equipment.
Safety has always been a major issue in paper manufacturing, but this is improving with initiatives such as the 1998 PABIAC (Paper and Board Industry Advisory Committee of the Health and Safety Commission) initiative to drive forward a 50% reduction in accident rates by last August, which this mill has met.
This has been in no small way, due to the fact that, with the Monitran vibration sensors installed on machinery it is now possible to monitor critical, difficult to access or hazardous areas remotely, simply collecting the data that is fed back to the switch boxes, installed in safe environments.
For example, Monitran MTN/1100CQ quick-fit accelerometers are installed to monitor vibration in areas such as the machine hood, which operates up to in excess of 30° C. Since an engineer’s presence is not required during the measuring procedures undertaken by these permanently mounted sensors, safety and convenience are greatly improved. This configuration also has the added advantage of supplying accurate diagnostic results as the data is collected from the same location on every occasion.
All of the bearings running on the actual paper machine are critical to its operation and the company cannot afford any unplanned downtime through failure. Every hour that a paper machine is down costs the mill around £6000- £10,000 in lost production, depending on the quality of the paper being produced. This does not include any labour costs involved in getting the machinery up and running again nor the possible damage to the equipment and the cost of replacement parts. The knock on effect of letting customers down and damage to the company’s reputation also needs evaluating.
In total the paper machine, encompasses 64 drying cylinders that are processing a 6.5 metre wide web, running at a speed of 650 m/minute, with drive bearings being monitored on all.
Furthermore, the Monitran MTN/1100CQ sensors are also playing a vital role in monitoring the performance of sealed fan and motor units, located in the plant’s environmental system, which is on the roof of the machine house.
Once again, the ability of the sensors to be hardwired back to the MTN/3000 switch box for data collection eliminates the need for any disturbance of the sealed fans and motors being monitored and reduces any risk to employees.
When specifying new plant, the paper mill requests, as standard, that all bearings used have the facility to be fitted with accelerometers for vibration monitoring as part of their predictive maintenance programme.
In addition to the MTN/1100CQ quick-fit accelerometers, a number of Monitran’s low profile MTN/1100SHC sensors are being used, for installation in areas where space is restricted. Typical installations at the plant include the monitoring of rotor bearings on screens in the process.
The data from the Monitran accelerometers is collected using a portable data collector from the MTN/3000 switch boxes and downloaded to a central computer for analysis and reporting. Frequency graphs from the bearings monitored provide the engineering team with an accurate representation of the current operating condition of the plant, from which maintenance requirements during the planned shutdown are scheduled, or if possible, repairs are made in safe areas while the plant is still running.
It is clear to see the substantial gains from implementing a condition-monitoring programme rather than operating a run-to-fail regime. The initial minimal outlay required to install and run a predictive maintenance programme represents a sound investment as opposed to running the risk of being unable to supply customers on time, and as profit margins become increasingly difficult to maintain it presents companies with the opportunity to prepare for essential repair work without threatening productivity or survival.
