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ivibr8

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Posts: 163
Reply with quote  #1 
Thought I would share a recent field balancing job and ask if any of our members have seen something similar.
Two days ago I was contracted to field balance a baghouse fan at a stone plant. This fan is used to remove lime dust from stone quarry mix. It is an overhung fan assy belt-driven by a 250HP motor. It had just failed its second set of bearings within a month. The bearings themselves did not fail but the interface between the shaft and inner race became loose (setscrew design). New heavy duty dual-row angular roller bearings installed with locking taper collar.

In short, I was not successful in balancing the fan. There was significant amount of axial vibration (27 mils) while the radial vibration was varying between 1.5 mils to 3.5 mils and phase very erratic.
The entire fan assy base plate was loose and causing the entire structure to be rocking: I measured at various locations along the vertical length of the structure (getting linearly higher as I measured up and all in phase).

 I really didn't expect to be successful but I tried to use the "average" values from the "O" and "O+T" data, but the two shots were not very effective. I essentially had a non-linear system.

What was confusing to me was that the the operators indicated the base has been loose for years and earlier in the year, the client's vibration guy was able to get levels down to less than a mil and according to him, it responded well to shots.  I struggled with trying to explain how the vibration increased when the balance condition had not changed. The speed is always the same. The damper position is always the same.  There were a number of things we looked at but no smoking gun.

Today, I went back to the Plant to retrieve some gear I left behind (yes, age has something to do with it). But I was glad I did. The fan (now in operation) was running very smooth!!!???  The operator thought it was because it was in normal operation. I didn't think this was likely as we changed damper settings from full open to full closed and I only measured minor effect. I could not think of any other force in play.

What I did notice was the the foundation plate had significantly lower movement. Why?
The only thing I could think of was last night's rain had soaked into the ground and around the foundation.  Could the rain actually act as a "coupling" agent between the known looseness?  Could this have changed the system response that much?
I asked the operator to notice whether the vibration comes back at the end of the day when it becomes "unloaded" or whether the vibration remains low.

So members.....has anyone seen or experienced something similar? Does it seem plausible to you that rain water can act as a good coupling agent, even if its temporary as drier conditions return?

Sorry for the long post.....but thought it be a nice topic for discussion and learning on my part

Regards
Jim Powers


John from PA

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Posts: 963
Reply with quote  #2 
This might get better visibility if placed in the Vibration Analysis - Balancing - Alignment forum at http://www.machineryanalysis.org/?forum=473361
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