Background

This case study is from a cement manufacturing plant located in Ireland, Europe.

Eastway has been providing services to this client both on request and planned for many years, including vibration analysis and thermography inspections.

Case description

In-house vibration monitoring detected high vibration values on this Fan unit and it was suspected that a fan imbalance was the cause of the vibration. The fan was then sand blasted by maintenance personnel, however vibration remained high. Then Eastway was called to measure the vibration on the fan and carry out a deeper analysis of the data.

This unit has one supply motor, a coupling and a fan shaft and impeller.

Machine Name

Fan 75261
Description Motor – Coupling -Fan
Motor Plate RPM 1479
Bearing – FNDE 22219EK/C3
Bearing -FDE 22219EK/C3

It was noted that the vibration was higher all around the unit. See Figure 1 for Motor Non-Drive Bearing Velocity Spectrum and Figure 2 for Fan Non-Drive Velocity Spectrum.

Time Waveform was mainly showing a sinusoidal pattern. The waveform length was matching with the 1X Fan, approximately 25.54 Hz.

To complement the analysis, cross channel phase readings were taken across different points of the unit. This analysis determined that the main cause of the high levels was due to an imbalance on the fan impeller.

Recommendation and Action Taken

Based on this analysis, it was recommended to carry out in situ fan balancing.

The procedure for balancing was done in one plane, following recommendations for the fan impeller dimensions. 36g of permanent weight was added in the blade marked as #6.

After the balancing completion, the vibration was tested across the unit and a significant reduction in vibration values was found. This reduction was up to 70% less vibration in some points of the machine. See table 1 below for more details.  

Location Before After Units % change
MNDE – Vertical 6.102 1.811 mm/s RMS -70.31%
Fan DE – Vertical 3.178 1.402 mm/s RMS -55.89%
Fan NDE – Vertical 6 2.566 mm/s RMS -57.23%

The two vibration spectrums below compare the change in amplitude for the 1X fan speed component of the unit on the Motor Non-Drive End side. Red arrow indicates the magnitude of 6.108 mm/s before the balancing. New after balancing value of 1.827 mm/s is indicated with a green arrow. The two graphs are using the same scale for easy visualisation of the change.

The resultant vibration levels are satisfactory according to the ISO standards recommended limits for industrial fans.