Ultrasound for bearing inspection
Pierre Langevin patented the first technological application of ultrasound during World War One by inventing a device to detect submarines. Like Langevin, maintenance engineers and plant managers can also use ultrasound for detection. Either by itself or as a companion technology, ultrasound can be an excellent part of condition monitoring for your bearings. Here, Chris Johnson, managing director at specialist bearings supplier SMB Bearings, provides an introduction into some of the benefits of this technology.
There are many ways of monitoring the condition of bearings and identifying potential defects. Traditionally, vibration analysis has been a popular option and infrared technology has also been used. Ultrasound, however, offers unique benefits that make it an especially useful tool for condition monitoring.
Ultrasound refers to high frequency soundwaves outside the range of normal human perception, typically in excess of 20 kilohertz. In the natural world some animals, like bats and porpoises, use ultrasonic detection for hunting prey. In industrial applications however, ultrasonic detection devices can allow maintenance engineers to ‘hear’ sounds that would otherwise be inaudible, including ultrasounds made by faulty bearings. Ultrasound devices translate these noises into the audible range through a process called heterodyning.
Ultrasound technology is arguably better than more traditional bearing inspection methods at identifying problems at the earliest possible stage and crucially, pinpointing the precise location of the fault. Sounds in the ultrasonic range have short waves, making them easier to separate from background noises like the normal running of machinery. The short waves do not spread out as rapidly, making it easier to identify the origin of the sound and therefore the location of the problem. These factors make ultrasound extremely effective at providing early detection and intervention.
Another undeniable advantage of this technology is its ability to monitor slow moving bearings. For all its benefits, vibration analysis is known to have limitations for bearings at lower speeds and as a general rule, these limitations increase the closer you get to zero revolutions per minute. If you are using slow moving bearings, ultrasonic sensors are more effective.
Ultrasound is also especially well-suited to identifying problems with lubrication. Research has shown that four out of every five cases of bearing failure can be attributed to problems with lubrication. When read with an ultrasound detection device, a properly lubricated bearing will provide a uniform reading. In the case of over lubrication, very little ultrasound will be picked up. For under lubrication, ultrasound will spot or ‘hear’ the problem before vibration analysis or infrared technologies that identify heat.
Ultrasound can therefore be used for condition-based maintenance, meaning relubrication can take place when a problem exists rather than being done automatically after a set period of time. As ultrasound identifies problems at such an early stage, there is also less need for interruptions to carry out relubrication. The early warning means the work can be carried out within the time put aside for pre-arranged maintenance schedules. Furthermore, ultrasound technology can allow technicians to better learn when to lubricate and how much lubricant to apply.
Further benefits of ultrasound include its ease of use, affordability, and versatility. Use of these devices does not require extensive training and they tend to be quite lightweight and portable. Ultrasonic detection can also be used for other maintenance tasks, like identifying leaks for example, making it a multifunctional and worthwhile piece of kit.
For maintenance engineers and plant managers, bearing faults can torpedo productivity, leading to costly unplanned downtime and hefty repair bills. Like Langevin, engineers can use ultrasound to detect the enemy — in this case a fault with their bearings.