Gearbox Wear Leading to Natural Frequency at a Cooler Fan

One of the most complicated and interesting challenge that we faced in IGS ….

That one of our esteemed clients called us for a repeated catastrophic failure of Cooling Fan of Extruder Main Drive Motor coupled with Reduced Gearbox.

The Problem was that during their normal routine vibration survey, they noticed that the overall vibration of the motor started to increase with strange frequency appeared in its’ Spectra “478 Hz” which does not match with any Motor Bearings Frequencies or other electrical or mechanical issues, Unfortunately there is no access to measure Gearbox or Extruder vibration due to the Installed Noise Hood around them.

The vibration increased to more than 12 mm/s RMS on inboard bearing till the motor cooling fan had been damaged suddenly before any preventive action.

They changed the cooling fan with new one, changed motor bearings and Re-aligned the machine as a corrective action and then run the machine back and observed its vibration behavior.
Unfortunately, The same Vibration behavior had repeated as it started with low amplitudes and increased over time with the same unknown frequency.

Here they decided to call us before ant repeated Failure of the motor fan …

IGS Team asked to remove the noise hood to measure the whole vibration of the machine. After taking all Safety Precautions, All Measurement had done and found the following:

There was a sign of teeth wearing inside the gearbox which created the unknown frequency 478 Hz as a gear mesh frequency with sidebands and Pure appearance of its’ impacts on time waveform.
The vibration transmitted to the Motor bearings and then to rotor which carried the Cooling Fan.
From the increasing of motor vibration which started with low amplitudes then increased to higher values, IGS suggested that the machine could go through one of its’ Natural Mode.

After applying a Finite Element Analysis by ANSYS and Me-Scope Software’s, we discovered that the 2nd Mode of Cooling Fan Natural Frequency matches with the gear mesh frequency which amplified due to the Teeth Damaged and transmitted to the Motor.

After Disassembling the Gearbox to replace the damaged gear, with some of mechanical measurements to ensure the whole condition of the gearbox, IGS found that There was a sever misalignment between Gears which lead the gear to be damaged.

Problem had been Solved and one of the most valued lesson learned is to install an online Vibration and Condition Monitoring System on Gearbox and Extruder to avoid any repeated Failures and keep monitor the Machine in Good Condition.

gearbox wear resonance fan