Detection of imbalance in critical process fan22 June 2022

An industrial plant specialising in building materials had an issue with a critical, interruption-insured 500kW process fan.

Even under normal process conditions, the fan blades kept fouling due to particles in the process air; this resulted in an imbalance. A regular cleaning routine was in place, and the fan was part of the route-based condition monitoring program. The troubling observation was that even with regular cleaning and balancing, the results were short-term, and the vibration levels held at a steady elevated level even after planned maintenance.

The customer concluded that the regular, manual inspection routine was not enough. The customer concluded that the regular cleaning and balancing did not expect results, or the impact was only short-term. With manual inspections, detection of cleaning needs was achieved, yet cause and effect were suspected to be only partially understood. To understand the situation in more detail, the customer contacted preventive maintenance consultancy Distence for options to gather more and better data to achieve a more comprehensive understanding.

The Condence blower monitoring concept was installed on the machine. Also, a Condence terminal and sensors were installed by the customer’s technician and analyses configured remotely with the assistance of the Condence team.

Once the first analysis results were received, it was clear that the regular cleaning routine for the machine was not enough. High vibration levels were especially evident during the coast-down period for weekend stops.

One of the automatic metrics in the Condence monitoring concept was an imbalance which is the amplitude at 1xRPM. The trend of this metric showed the customer that the process fan was running at levels that would shorten the useful life of the fan. When comparing the results between the four installed sensors, the vibration levels are highest when measuring the bearing closest to the fan wheel. In comparison, the measurements from the electric motor were slightly elevated but acceptable. Measurements also showed that the regular cleaning did not noticeably decrease the vibration levels.

The customer decided that the process fan required more thorough cleaning and rebalancing. The decision to perform corrective actions during the next weekly break was made, and the activities were completed for the next production week. Cleaning and rebalancing brought the vibrations levels down drastically.

Verifying the results of actions and making it easy to track the condition of the device in the future made the job of scheduling necessary maintenance straightforward. Now, those actions can be based on the actual state of the fan. With such successful efforts, the customer could add years to the machine’s remaining useful life. The graphs show the trend of the imbalance metrics, and the spectrum of the measurement point with the most severe vibration levels.

Fans and blowers may be challenging to access as they are commonly mounted to the ceiling or roof. It makes them difficult and potentially unsafe to monitor with manual route-based vibration devices, but ideal for remote online condition monitoring.

Operations Engineer

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