Hoping you can help me with a overhung fan which has an increasing 3x fan frequency which is dominant in the axial direction.
Overhung Fan which cartridge containing 2 x 6310 bearings.
Fan was rebuilt around 4 months ago where motor was replaced (old motor was 37Kw), New pulleys, new belts, new fan shaft, rebuilt impeller and new bearings in existing cartridge.
Recently vibration is showing an increasing frequency at what could be either 3xF or BPO for the 6310 bearing which is highest at the fan side bearing. The fault does not appear to be a bearing as there is no harmonic series nor are there any indications of a BPO in the demodulation. The amplitude of this frequency is currently 10.98mm/sec RMS. Thermal imaging of the cartridge shows an even temperature of 32 degrees C with a 19 degree ambient. This frequency appears in all locations but increases the closer you get to the fan impeller. (i.e. you can see it in the belt side fan bearing @ 3.68mm/sec RMS.
During our inspections we also noted that the motor DE bearing appears to be on the hot side at 73 degrees C with 19 degree ambient but no evidence of any issues in the vibration.
We reported the fan fault last survey and told the customer to inspect the belt drive pulleys for runout, belts and fan shaft for wear etc. Customer reports that no faults were found during their inspections.
I have read some case studies of air flow issues in overhung fans causing high 3xF in axial direction but I don't see any raised floor noise in sub run speed frequencies.
Any ideas you may have would be greatly appreciated