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Danny Harvey

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Reply with quote  #1 
I have a lcient who suspects severe soft foot in a fan motor slide base and wants to monitor the 2 x lf while we loosen motor/slidebase bolts to measure reaction.

Is this safe? Is it going to tell us anything about softfoot or will the belt pull counter the frame distortion?
RustyCas

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Reply with quote  #2 
Personally, I wouldn't have a problem loosening 1 bolt (of 4) at a time, or 2 on the side the belts are pulling towards.  Where is the problem vibration showing up?  I would much prefer to do this "off line" when I have the time and ability to look at everything closely.  If the soft foot is actually "severe" then when everything is unbolted it will be obvious, and it it's not obvious, then it's probably not severe.  

I can only recall "soft foot" causing a severe vibration problem on 2-pole motors, very large motors with a "cradle" arrangement (instead of a solid stator), and a centrifuge mounted on rubber isolators. But I suppose a slide-base could cause a problem. Maybe.

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Danny Harvey

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Reply with quote  #3 
Safety aside, would you think that the motor frame would accurately react or would the belt pull alter the forces enough to alter it's reaction?
MachDiag

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Reply with quote  #4 

Most adjustable motor bases are pretty flimsy these days, probably a good chance the base is more flexible than the motor frame.  Got a picture of the suspect base?

You could certainly loosen 1 bolt at a time and watch what happens, things really shouldn't get out of hand by doing this.  The vibration reaction of doing this will likely be quite different than when it's done on coupled machinery.  I'd probably exhibit to see multiples of drive speed as a result of the temporary looseness that is created. 

V-belts can be outstanding vibration producers, maybe make sure a multiple of v-belt speed isn't looking like 2x motor speed.

If I could get a shutdown, I'd prefer to do the soft foot check then and fix it on the spot.    

 

 

 

        

Danny Harvey

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Reply with quote  #5 
We were given 1 hour to shut it down. Found .015" soft foot. .017" axial motor sheave runout (cocked bushing), worn belt, misaligned fan rotor.

Fixed the soft foot, fixed the sheave runout, put the motor back in it's original position and all vibration amplitudes dropped drastically.

Thanks for the quick responses.

The still need to clean the fan rotor, check the fan rotor to fan housing alignment, level the fan rotor, replace the belt, then they can get a proper belt alignment by moving the motor.

Danny Harvey

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Reply with quote  #6 
Thanks again.  You guys helped us restore some credibility to a floundering program.
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