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Xracer

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Reply with quote  #1 
I have attached a recent fan balance job that was done and have a question or two on heavy weight position. 

This was a overhung fan wheel, backwards incline airfoil blade style. 9 blades. Laser(tach) was set up in the 3 O'Clock position and both channel 1 and channel 2 accels were placed at the 3 O'Clock position (Horizontal). 

The initial run shows 1.9 mil @ 175 deg (Ch1). Since I have it set up as with rotation, would this indicate that the heavy spot is a 175 deg with rotation? This would put it at 4.375 blades past #1 or roughly blade #5. 

When the trial weight was added, amplitude increased to 3.1 mil @ 162 deg. This would put the heavy @ 4.05 blades past #1 or blade #5?


This was done with a VB7..


 
Attached Files
pdf Example.pdf (916.18 KB, 36 views)

fburgos

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Reply with quote  #2 
final vibration went down, Congratulations good job.

for me is unatural to first blade be 0° and angle increas in direction of rotation.

you want to lower vibration on trial run, then

heavy spot= phase - lag + sensor angle + integration angle

in your example HS=178-lag+0+0

trial location=HS+180°=178+180-lag.

I have always wanted to know how we get the lag, usually I just add my trial opposite to the heavy spot and keep the instructions on screen

In your example I would add my trial at the blade inline with reflective tape.

PS: I like last blade 0° and angle increase against rotation but thatis another topic
Xracer

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Reply with quote  #3 
Quote:
Originally Posted by fburgos
final vibration went down, Congratulations good job.

for me is unatural to first blade be 0° and angle increas in direction of rotation.

you want to lower vibration on trial run, then

heavy spot= phase - lag + sensor angle + integration angle

in your example HS=178-lag+0+0

trial location=HS+180°=178+180-lag.

I have always wanted to know how we get the lag, usually I just add my trial opposite to the heavy spot and keep the instructions on screen

In your example I would add my trial at the blade inline with reflective tape.

PS: I like last blade 0° and angle increase against rotation but thatis another topic


On this example, my trial weight was added to blade #1 which was inline with the reference mark(tape). 
I'm still trying to grasp were the "true" heavy spot is during initial and trial weight runs.. 
 
RustyCas

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Reply with quote  #4 
Fan speed? Approximate size (weight & diameter)? Type support (metal A-frame, mounted on ground or on a “tower”)? This is one of my favorite topics - will be happy to illustrate my process.
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John from PA

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Reply with quote  #5 
Quote:
Originally Posted by RustyCas
Fan speed? Approximate size (weight & diameter)? Type support (metal A-frame, mounted on ground or on a “tower”)? This is one of my favorite topics - will be happy to illustrate my process.


From the report, the speed for the balancing was 1683 RPM.
Xracer

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Reply with quote  #6 
Quote:
Originally Posted by RustyCas
Fan speed? Approximate size (weight & diameter)? Type support (metal A-frame, mounted on ground or on a “tower”)? This is one of my favorite topics - will be happy to illustrate my process.


Rusty,

This was a Kice fan. Approx wheel diameter would be 36" X 10". (Rough memory measurements) . I dont have the weight of this rotor. I can see if Kice will provide me with the weight. If the wheel was removed, we would have checked the weight.. 

Pic of fan type. Mounted on rubber vibration violators.. 
Fan.jpg 

Ralph Stewart

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Reply with quote  #7 
Can you answer the question in the original polar plot you posted?

They may be already answered but I was unable to "find" them.[smile]

Thanks,
Ralph

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jpeg Polar Graph Questions.jpg (98.37 KB, 14 views)


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Xracer

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Reply with quote  #8 
Quote:
Originally Posted by Ralph Stewart
Can you answer the question in the original polar plot you posted?

They may be already answered but I was unable to "find" them.[smile]

Thanks,
Ralph


Here you go. This is how I had the equipment setup.. Tape at 0 (blade #1)  and tach/accels set at 3:00.. 

Setup.jpg 

Ralph Stewart

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Thanks Xracer. [smile]

Ralph


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Ralph Stewart

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Reply with quote  #10 
Xracer quote:

Quote:
On this example, my trial weight was added to blade #1 which was inline with the reference mark(tape). 
I'm still trying to grasp were the "true" heavy spot is during initial and trial weight runs..


Your TW1 weight, based on your data, caused a 13.5 degree Phase change and a 1.2 amplitude increase, which says, to me, the TW1 was placed almost on top of the Heavy Spot.

Your "Heavy Spot" was in the same position on the fan during your runs [smile], just that the phase had shifted from the Below Critical position to the Above Critical position. Basically giving the wrong information when assuming it was running below the 1st critical frequency. Absolute below critical speed usually ends up with the light spot being 180 degrees from the degrees the analyzer shows, (1.9 @ 175 +180)

  This opinion is based on my experience and on what I get from the "theory" of phase verses critical frequency speeds,

Phase Shift:
           0 = below,
          90 = at, (most difficult position to do a balance)
   and 180 = above
the 1st critical frequency speed.

IMO, a "test" should be done on each balance job, if possible, prior to attaching the 1st trial weight. Reason is, too much weight in the wrong position could cause serious problems.

Just my opinion and I could be totally wrong.

Thanks,
Ralph

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Walt Strong

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Reply with quote  #11 
"This opinion is based on my experience and on what I get from the "theory" of phase verses critical frequency speeds,"

My opinion is that adding, subtracting or moving balance weights does not have any (significant) effect or change to critical speed or "balance resonance".

Walt
OLi

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Reply with quote  #12 
It may however change the speed, normally not that much but noticeable. I am not sure in this case and unless a very sharp resonance it should not shift that much but in some cases when speed is not repeatable and not stable it may give trouble so you need to look at the polar plot.
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