Under lubricating or overlubricating a bearing can destroy it and bring production to a halt. Although there’s always going to be a certain amount of friction, maintaining just the right quantity of lubrication will keep it at an acceptable level.
In his July 2021 Accelix best practices webinar, Blair Fraser, global director of IIoT Solutions at UE Systems Inc., demonstrated real-life examples of how to use ultrasonic technology to detect the early stages of bearing failure and root out the cause. Attendees learned how to use it to monitor, detect, and analyze bearing health data to prevent a fault before it occurs.
IIoT drives an increase in ultrasound advancements and capabilities
A daunting eighty percent of premature bearing failures can be traced to over-or under lubrication. By combining an IIoT system with real-time friction and impact monitoring, ultrasonic technology can catch the signs of a bearing defect early. Ultrasound measures the decibel or sound level of friction, and impacting indicates it needs lubrication.
In addition to over-or under-lubrication, bearings also fail due to contamination, using incorrect grease, material defects, and indirect causes such as improper machinery mounting. But over greasing often has the most detrimental effect on bearing life.
Ultrasound and the P-F curve
An ultrasonic sensor can detect friction by focusing on a narrow band of high-frequency sounds inaudible by humans or even dogs. Ultrasound technology isn’t new. The capabilities have been recognized for decades in academic studies, and more recently, within the medical and food industry. Recently, it has resurfaced as an excellent way to prevent premature bearing failures thanks to enhanced sensor capabilities and technological advancements.
The P-F curve shows the window of opportunity for identifying impending bearing problems using ultrasonic technology instead of vibration or temperature monitoring, which reveal problems later on.
The sooner you can uncover a bearing issue, the better. Even if you cannot identify the exact cause of the fault, just knowing that maintenance is needed can avoid a potential catastrophic failure, safety issue, secondary machinery damage, or unplanned downtime.
Time-based calculations for determining lubrication maintenance can be very complex. No two bearings are manufactured, installed, or greased the same, so baselines can vary, making setting the perfect limits challenging. Furthermore, correction factors are essentially assumptions because the lubrication frequency cannot account for changing operating and environmental conditions.
Monitoring friction is key to sustaining bearing health
If your bearings could talk, what would they say? Fraser suggests letting friction tell you when your bearing needs grease and when it’s not sustaining its properties.
The ISO29821-1 standard dictates when to lubricate a bearing based on decibels above your established baseline. For example, an +8 dB increase indicates that it needs lubrication. A 16-decibel reading indicates early onset failure, and a 35-decibel increase means it’s close to failure. This range changes somewhat depending on the bearing type.
Setting and trending near the baseline
When applying ultrasound technology, use the recommended thresholds and then trend the sensor data over time to ensure you’re getting an accurate baseline. This sensor system software enables you to watch the arrow and status move downward or upward in real-time using a laptop, mobile device, or computer. Depending on your setup, you can add grease remotely using an automatic lubricator.
Trending healthy and unhealthy bearings
A healthy, well-lubricated bearing will have a steady friction trend with peaks and valleys less than 4 decibels. In this example, once the bearing was lubricated, there was a noticeable decrease in friction. The level returned to the baseline, going from 29 decibels to 16 decibels and stayed there, indicating the bearing was healthy.
Unhealthy bearings will have friction bouncing around, producing more significant peaks and valleys caused by impacts of rolling elements. Once you lubricate, it’s critical to ensure that levels remain constant. Fraser provided an example of an unhealthy bearing, which, when greased, took friction down to an acceptable level. However, within a few hours of lubrication, the levels went back up.
The customer continued to lubricate, but an acceptable friction level could not be sustained, indicating an unhealthy bearing. It’s critical to continue to monitor friction to make sure levels stay steady.
Ultrasonic analysis enables you to gain deep insights into bearing health. For more guidance on applying ultrasound technology to prevent bearing failures, watch the entire webinar at Accelix.com.