Maintenance Technology August 2014 - (Page 27)

FUNDAMENTALS 3. Regular comparison of the operating temperature of a single unit to previous images of the same unit Since the thermographer guides the infrared inspection process, his/her knowledge is of the utmost importance. Thermal imaging can be used to identify several conditions such as inadequate airflow, unbalanced voltage, impending bearing failure and insulation degradation in a motor's rotor or stator. It can also identify heat produced by shaft misalignment. Regardless of the application, however, the final results of a thermographic inspection depend upon understanding the task to be performed, selection of equipment, operator skills, inspection techniques and documentation of findings. Before embarking on an inspection, a thermographer needs to consider and understand how these factors will influence final results. The following steps outline the basic elements a thermographer needs to consider for a successful inspection in any environment. Define the task Perhaps the most important-and often most overlooked-part of thermography is the need to define the project. Before any successful task can begin, the thermographer must determine exactly what is to be done and what is expected of the final results. In the case of routine inspections of industrial equipment, this will typically be understood. Infrared can and should be included in normal maintenance "rounds" to establish benchmark results for ongoing comparison. In non-routine situations, however, specific details are needed to ensure a useful inspection. For example, a thermographer may be asked to "conduct an infrared scan to locate wet areas" on a facility's roof, a request that does not adequately define the task. It is unclear when the work is to be performed, what type of imager is be used and what type of documentation may be required. But regardless of inspection type, it is always desirable for the thermographer to fully comprehend all aspects of what is expected. If the inspection requires skills beyond thermography, the thermographer, if qualified, may elect to perform these tasks or work with others who are qualified. Once the exact nature of the task has been determined, a scope of work can be developed. Thermographer qualifications The operator may be the greatest limiting factor in thermography. Although thermal imagers have AUGUST 2014 IR Imaging Gives Fast Results on Gearbox Health The ability to determine lubrication health is another key IR capability, and should be included in any PdM program. The lifeblood of any gearbox is the oil that lubricates its gears. If oil loses its ability to lubricate-or the level of oil gets too low- the gearbox will overheat and eventually fail. Traditional preventive maintenance for gearboxes has consisted of regular oil-level checks and replenishments as needed. Some maintenance departments add a predictive element to gearbox maintenance in the form of oil sampling and analysis. Oil analysis, usually performed by an outside laboratory, reveals if the oil in a gearbox has lost its ability to lubricate. It will also detect any metal particles in the oil, a sign of gear wear that foreshadows possible failure. While effective, oil sampling is relatively time-consuming, and can be costly. It can also require equipment shutdown. Moreover, gearboxes often are inaccessible or in unsafe locations, which can make oil-level checking and oil sampling difficult. For these reasons, thermal imaging is a good alternative PdM approach. Since gearboxes generally overheat before they fail, an infrared (IR) camera can detect when a unit is running hotter than normal and/or hotter than similar gearboxes performing similar work in similar environments. Because thermography is a non-contact, non-destructive technology, even inaccessible gearboxes in dangerous locations can be scanned while running. The IR camara can be used to capture all thermal images as well as visible-light digital images of all units that are running hotter than normal. These processes can also reveal leaking seals where hot oil is running down the sides of gearbox cases. Be aware that any excessive heat generated in mechanical gearboxes is the result of friction, and that inadequate lubrication is not always the source. The cause could also be faulty bearings, misalignment, imbalance, misuse or just normal wear. Still, thermography is a good first step toward a complete analysis of the condition of any gearbox. Source: Fluke Corporation their limitations, thermographers can overcome this by selecting the proper equipment (discussed later). Since the thermographer is the most important factor in thermography, knowledge is of the utmost importance. Unless otherwise specified, it is usually not enough for a thermographer to understand only how to operate a thermal imager to produce thermograms. At a minimum, the thermographer should have completed a Level I thermography training course. Thermographers who perform inspections involving temperature measurement should be trained to at least Level II. The professional thermographer needs a thorough understanding of infrared theory and heatMAINTENANCETECHNOLOGY.COM | 27 http://www.MAINTENANCETECHNOLOGY.COM

Table of Contents for the Digital Edition of Maintenance Technology August 2014

Maintenance Technology August 2014

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