Unwind Drive Cooling Fan ©Bill Kilbey 2009

High 1x Cooling Motor/Fan Motor/fan sit on top of large variable speed motor, fan mounted directly on motor shaft The fan is subject to buildup of dirt/product 1x TS dominant with amplitudes increasing Attempt to balance was not successful – Varying amplitude 1mil pk-pk to 7mils pk-pk – Unstable phase ±100⁰

High 1x TS

Unsuccessful balance attempt Amplitude and phase both unstable I tried the lowest filter band % on the tach, still no luck

High Resolution Spectrum

High Resolution Spectrum Zoom

Spectrum from other cooling fan

Calculations – = 3.8 RPM Delta (.063 Hz) The inverse of Diff. F1-F2 = T beat T beat = 15.8 secs. approx.

Time waveform beat on #2

Time waveform beat on #3

#2 PM Fan #3 PM Fan

Conclusions The cooling fans are exciting resonances of the respective motor and foundation. You can feel the vibration and beat in the floor. The 2 fan speeds are beating, they are physically locate 30’ apart. Band filter on tach is not fine enough to separate 4 RPM. Rebalance attempt on day when both can be shut down. Investigate foundation and structure for resonance.

Update 11/3/09 #2 is shut down, so no beat. Can not shut down #3 for balance. Data shows bearing may be slightly loose in housing. – RBPF and 1x TS sidebands have increased – PeakVue has High 1x TS and small bearing defects. Looseness may contribute to phase/amp instability.

Balance Reference Run Original with beat Today with no beat 3.3

Rotor Bar Pass Freq. w/sidebands 1xTS

PeakVue 1x TS and harmonics