May 2020

images. Part of the outer race came away as it was opened. It was also noticeable that one of the rollers had moved 90 degrees. The cage had been totally damaged too. Ultrasound and slow speed bearings – the method As we can see, ultrasound technology is very useful when trying to monitor the condition of slow speed bearings, and an ultrasonic instrument/sensor is able to provide maintenance personnel with a warning of failure, even in extreme slow speeds like in this case. With bearings rotating at normal speeds, ultrasonic inspection can be performed by comparing changes in dB values, establishing that a bearing with a certain value above a decibel baseline will need lubrication or be already in a failure state, depending on how much decibels it is above the baseline. However, with slow speed bearings, comparing dB levels and establishing alarms is not enough: in many situations the difference in the dB levels will not be significant or even non-existent, in which case the inspector might think there is nothing wrong with it. For slow speed bearings, one must rely on the sound quality and the sound pattern. For this, it is necessary to use an ultrasonic instrument with sound recording capabilities, like the Ultraprobe 15000, and then analyse the sound file on a sound spectrum analysis software like the Spectralyzer from UE Systems. Then, maintenance professionals can simply record the sound produced by a slow-speed bearing, load the file in Spectralyzer and analyse it in the Time Series view. The spectrum analysis of this oven motor bearing shows clearly where the roller at 90 degrees hits the crack as the knock stops briefly. Thus, the sound pattern indicates already an existing problem, being the most reliable source of information when determining the condition of a slow- speed bearing using ultrasound. On the other hand, the spectrum of a recorded sound from one of the “good” bearings shows a very different picture: a very uniform spectrum with almost no changes in the amplitude. This find has saved the company a significant amount of money, as it was necessary to get cranes in to replace such a big bearing, a job that took up to six hours. Luckily this was done during a planned outage, avoiding the costs of unplanned downtime. 24 | Plan t & Works Engineering www.pwemag .co.uk May 2020 Process, Controls & Plant Focus on: Seals,Bearings & Lubrication Sound Spectrum of a “good” bearing. Very uniform and no changes in amplitude. Join us on Facebook Plant &Works Engineering Follow us on LinkedIn Plant &Works Engineering Followus on Twitter @PWEmagazine1 @PlantAssetMgt For the latest news visit the PWE website www.pwemag.co.uk Find out the latest on Plant &Asset Management 2021 www.mai te anceuk-expo.com PWE Plant & Works Engineering Plant & Asset Management 2021