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June 11, 2026

Lubrication Data Reveals Suspected Fan DE Mechanical Looseness

Motor Direct-Drive Fan Assembly | Rock Crushing Plant | SDT340

The SDT340 LUBExpert Mode guides technicians through lubrication tasks while collecting dynamic data that can be reviewed later as part of a larger condition monitoring investigation. This case study follows a motor direct-drive fan assembly at a rock crushing plant. There was no historical ultrasound, vibration, or lubrication data available for the technician to baseline with. Each measurement served two purposes: support the lubrication decision in the field and begin building a baseline condition monitoring record. The route included four points in the following order: Motor NDE, Motor DE, Fan DE, and Fan NDE. The time waveform data was used to compare friction response before and after lubrication. The FFT spectrum data was then used to look deeper for mechanical patterns that lubrication may reduce, but not correct.

Time Waveform Summary

1. Lubrication Response: Before and After Time Waveforms

When no historical data is available, the safest approach is to let the bearing response guide the lubrication decision. The process begins with an initial ultrasound measurement to establish the starting condition. A small amount of grease is then applied, followed by another measurement to see how the bearing responds. If ultrasound levels decrease, lubrication can continue in controlled steps. If levels increase, lubrication should stop to avoid over-greasing or creating additional stress on the bearing. This step-by-step method turns lubrication into a measured decision instead of a fixed-volume task. Each before-and-after time waveform helps confirm whether the bearing accepted grease, rejected grease, or required further investigation.

Motor NDE Bearing - Time Waveform Review

Figure 1. Motor NDE Before Lubrication - Time Waveform.
Figure 2. Motor NDE After Lubrication - Time Waveform.
The Motor NDE bearing started at 39.31 dBuV and finished at 39.78 dBuV. Because the reading increased slightly rather than decreasing, lubrication was stopped. Some repetitive events were visible, but nothing clearly aligned with a bearing defect or looseness pattern at this location.

Motor DE Bearing - Time Waveform Review

Figure 3. Motor DE Before Lubrication - Time Waveform.
Figure 4. Motor DE After Lubrication - Time Waveform.
The Motor DE bearing showed a similar response, increasing slightly from 40.61 dBuV to 41.05 dBuV. Lubrication was stopped after the small rise in friction. This point was closer to the fan side of the assembly, where running speed activity began to become more relevant in the dynamic analysis.

Fan DE Bearing - Time Waveform Review

Figure 5. Fan DE Before Lubrication - Time Waveform. 
Figure 6. Fan DE After Lubrication - Time Waveform. 
The Fan DE bearing showed a strong lubrication response. RMS dropped from 67.10 dBuV to 59.38 dBuV, confirming that grease reduced friction. However, the later spectrum review showed that the mechanical looseness pattern was still present even after lubrication.

Fan NDE Bearing - Time Waveform Review

Figure 7. Fan NDE Before Lubrication - Time Waveform. 
Figure 8. Fan NDE After Lubrication - Time Waveform. 
The Fan NDE bearing also responded well to lubrication, dropping from 62.29 dBuV to 50.49 dBV. The reduction confirmed a successful lubrication response, while the later spectrum review showed the same running speed pattern at a lower level than the Fan DE bearing.

2. Transition: From Lubrication Task to Dynamic Analysis

The time waveform data confirmed whether each bearing accepted grease, but it did not tell the whole story. Because the SDT340 LUBExpert Mode can save dynamic signals during the lubrication task, the same measurements can be opened in the FFT spectrum for more advanced analysis. In the spectrum views below, the y-axis is shown as uV^2 (env. PSP), which represents the energy or power of the ultrasonic signal after envelope processing. This is why the fan spectra appear on a much larger scale than the motor spectra. The fan bearings generated much more ultrasonic energy before lubrication. Lubrication reduced the overall signal energy significantly on the fan bearings, but the running speed pattern remained visible. This is the key finding: grease reduced friction, but it did not remove the underlying mechanical looseness signature. In other words, lubrication may have masked the severity of the issue, but it did not correct the fault.

Motor NDE Bearing - FFT Spectrum Review

Figure 9. Motor NDE Before Lubrication - FFT Spectrum. 
Figure 10. Motor NDE After Lubrication - FFT Spectrum. 
The Motor NDE spectrum did not show the same strong running speed harmonic pattern seen on the fan side. This helped establish that the suspected looseness was not strongest at the far motor end of the assembly.

Motor DE Bearing - FFT Spectrum Review

Figure 11. Motor DE Before Lubrication - FFT Spectrum. 
Figure 12. Motor DE After Lubrication - FFT Spectrum.
The Motor DE spectrum began to show more relevant running speed activity as the measurement location moved closer to the fan. This suggested the pattern may have been transmitting through the machine train from the fan.

Motor DE Bearing - FFT Spectrum Review

Figure 13. Fan DE Before Lubrication - FFT Spectrum. 
Figure 14. Fan DE After Lubrication - FFT Spectrum.
The Fan DE spectrum showed the strongest evidence of the suspected issue. A dominant peak at 1X running speed with harmonic activity remained visible after lubrication. The overall energy dropped dramatically after grease was applied, but the looseness pattern was still present.

Fan NDE Bearing - FFT Spectrum Review

Figure 15. Fan NDE Before Lubrication - FFT Spectrum. 
Figure 16. Fan NDE After Lubrication - FFT Spectrum. 
The Fan NDE spectrum also showed running speed activity, but it was much less pronounced than the Fan DE bearing. This supported the conclusion that the looseness was most likely located near the Fan DE bearing and transmitting through the fan assembly.

Conclusion: Lubrication Data as Condition Monitoring Insight

This case shows why lubrication data should not be treated as a simple record of how much grease was applied. The motor bearings did not show a positive friction response, so lubrication was stopped. The fan bearings did respond to grease, but the dynamic data revealed something more important: a suspected mechanical looseness condition near the Fan DE bearing. The Fan DE bearing showed the strongest 1X running speed impact and harmonic activity. The same pattern was visible but less pronounced at the Fan NDE bearing, and it was weaker or less relevant at the motor bearings. Comparing the same pattern across the full motor direct-drive fan assembly helped localize the suspected source of looseness. For maintenance teams, this is the value of combining ultrasound-guided lubrication with dynamic analysis. Grease can reduce friction and lower overall signal energy, but it cannot correct mechanical looseness. By saving and reviewing dynamic lubrication data, teams can identify issues that might otherwise be temporarily masked by lubrication and missed until they become more severe.