Bearing Lubrication & PdM Using Ultrasound

In the maintenance and reliability industry, we see certain shifts in the functionality of our people, processes, and procedures for predictive, preventative, and reliability centered maintenance. We tend to focus on hot topics and buzz words that are pitched to push technology, drive innovation, build sustainability, but before we can tackle the bigger issues, we must first start with the basics. The basics of knowing your assets, extending the life of your assets to their full potential, and maximizing production. How do we extend the life of our mechanical assets using ultrasound technology? Many maintenance & reliability professionals refer to the D-I-P-F Curve as illustrated in Figure 1.

Figure 1: D-I-P-F Curve

The D-I-P-F curve is a model that represents the life of mechanical assets. Starting with Design, if an asset is designed to fail, it will fail. So, we either design our assets to be more reliable and maintainable, or we modify our existing assets to be more reliable. In Point I, or Installation of our assets, preventive measures are taken to make sure that our assets are installed correctly to eliminate any potential infant mortality related failure modes. What technologies are we using to make sure the asset is properly installed? Is the operator competent enough to effectively execute the preventative tasks? In the Proactive Area, ultrasound assisted bearing lubrication can help to play a role in extending the life of the bearing. Structureborne ultrasound is a great tool to help assist with over and under bearing lubrication. When bearings are in need of lubrication, there is an increase in friction. We can monitor the bearing decibel (dB) levels using ultrasound to know when the bearing is in need of grease, and to know when we have applied enough grease. Once implemented, this approach can help to move from time based lubrication to condition based lubrication. Next along the curve is Point P, or where we have the first instance of a potential failure mode. What predictive technologies can we use to help determine the condition of the asset, and what are the failure modes that the chosen technology will detect? Structure-borne ultrasound has become a proven technology to show when bearings are in an early stage of failure or fatigue. When ultrasound is used to trend bearing decibel levels, it can be a good leading indicator of a potential problem. The graphics below represent a dB trend when using ultrasound for bearing condition monitoring. All of these efforts work together to extend the life of the asset, and avoid point F or Functional Failure when the asset can no longer perform the way that it was designed and installed for.

Figure 2: Trend of ultrasound decibel (dB) levels for a bearing

Figure 3: Bearing decibel level alarm level settings:

When a bearing is 8 dB above our baseline, it is in a lack of lubrication state, and grease is added until the dB level is back to the baseline level. If too much grease is added, the dB will start to increase, giving us an indication that no more grease should be added. If there is no change in dB, then a follow up inspection with a complementary technology should be used to help determine why there was no change in dB while greasing.

Figure 4: Time Wave Form of a bearing in the process of being lubricated:

Figure 5: Time Wave Form of a bearing that has been over lubricated:

If the bearing has entered a failure mode that is beyond a lack of lubrication, we can use other technologies such as vibration analysis, infrared thermography, or an ultrasound instrument with onboard sound file recording to capture FFT & Time Wave Form data to try to determine what the failure is. The technologies that we use are helping us turn our maintenance practices from run to failure to a more proactive and predictive approach. Keep in mind that technology is only as good as the operator behind it. Creating awareness, buy-in, and education, and making good use of the data is what will drive the industry to a more reliable, predictable, and sustainable future.

Ultrasound instruments today, offer a wide range of features such as onboard spectrum analysis, spot radiometer for taking temperature readings, strobe to measure rpm, and digital camera for recording visual inspection information of equipment conditions. Ultrasound is also considered to be the most versatile of PdM technologies due to the variety of applications that the instruments can be used for. From compressed air leak detection, electrical inspection, valve & steam trap inspection, and bearing condition monitoring, any maintenance & reliability program can benefit from ultrasound. With new advancements in ultrasound instruments and sensors, ultrasound is poised to have a large impact in remote continuous monitoring applications and new asset management methodologies related to IIoT and Machine Learning.