Vibration analysis is a proven technology to predict machine failure and detect the root cause of the problem. Once a failure mode is detected it is important to understand and eliminate the source to maximize the life of the machine.
A food processing facility was experiencing high vibration levels in a motor-pump assembly with an integrated gearbox. It was evident from listening to the machine that there was a vibration problem, and leaking lubricant suggested there was a failing pump seal. The machine was rated for three-years but was only six months old when issues began to present.
Our Initial Suspicion
To get to the bottom of the issue, we utilized our VibePro 8 iPad program with a GTI-220 wireless sensor to capture a snapshot of the vibration in a waveform display. This visual allowed us to see the amplitude of the machine across a predetermined timeline. Our initial analysis led us to the conclusion that the vibration was caused by a broken gear tooth. Utilizing the circular time waveform function in VibePro 8, we compared the waveform imagery of the vibration from the broken gearbox with historical data of functioning gearboxes to confirm our diagnoses. The pattern for a well-maintained gearbox is symmetrical, but the data we were viewing was jagged.
Getting to the Source
Simply replacing the damaged gear would have only been a temporary fix. We knew for certain that the pumps were only lasting 20% of their rated life-span, so we needed to diagnose the root cause of the damaged gear tooth. We used Fast Fourier Transform (FFT) technology to convert the waveform data into acceleration data to provide more information and reveal new problems.
The acceleration data revealed peaks above 50 kHz–a clear sign of cavitation. Cavitation occurs when there is more air in a pump than fluid. The air bubbles act as an abrasive and wear away at the impeller and pump seals. Velocity data showed the vibration in terms of running speed in inches per second (IPS). The velocity data showed us which running speeds generated the most peaks. This illuminated the looseness and alignment issues in the pump and gearbox assembly.
Diagnosis & Conclusion
We concluded that the cavitation caused the seal to fail, and the vibration from the cavitation caused the looseness of the entire system. The looseness was responsible for the chatter in the gearbox which resulted in the cracked gear teeth. The problem was likely present from the initial install, so we advised changing the size of the impeller to better fit the application and replacing the damaged parts.
If we had just replaced the broken gear component from the beginning the manufacturer would have been back to square one very quickly, as the source of the problem (the cavitation) would have resulted in the same incremental damage. This cycle of temporary fixes would have cost more money in labor and material costs. However, thanks to the in-depth scope of the VibePro 8 platform, we were able to go deeper than the surface problems to identify the root cause of the issue and prevent future breakdowns from occurring.
About GTI Predictive Technology
At GTI Predictive Technology, it is our mission to provide the best predictive tools on a single iPad platform with services to monitor nearly any asset. We strive to bring our customers the portability, connectivity, and affordability offered by the latest available technologies. Our product family combines wireless portable and online vibration data collection and analysis, balancing, shaft alignment, thermography, and ultrasound into an affordable and completely scalable solution on one simple to use platform. GTI’s predictive technology apps feature many additions that have come directly from customers. Click here to learn more.