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Dear Forum members,

Good Morning,

I am a balancing engineer and i do balancing by reducing Housing vibrations. and if  i reduce these housing vibrations even shaft vibrations will come down.

But in some rotors if housing vibrations are high, shaft vibrations will low vibration, after reducing housing  vibrations also if shaft vibrations are not coming down, we have to select directly do correction on shaft vibrations,

Generally we use LP side x and y probes and HP side x and y probes.

How to select, which one to select or we have to select higher vibrations x or y or both.

Can any one suggest procedure to balance a rotor by using shaft vibrations by using vector method or with the help of any software in step wise.

regards,

D.Ravishanker

 

 

Original Post

D.Ravishanker,

As you know, rotor unbalace can result in high vibration measured on the shaft and bearing housing. Also, unbalance vibration can be reduced by balancing using readings from the shaft or the bearing housing.

However, the amplitudes on the shaft and bearing housing may not necessarily agree during balancing. Also keep in mind that correct balancing will reduce 1X related to unbalance and may not affect other causes or frequencies.

So, if you have doubts because of conflicting data, it is worth asking the owner for what matters most. For example, if the online protection system is only for shaft vibration, the owner may see that as more important than casing vibration.

Regards- Ali M. Al-Shurafa 

As you know, rotor unbalance can result in high vibration measured on the shaft and bearing housing. Also, unbalance vibration can be reduced by balancing using readings from the shaft or the bearing housing.

When you do this in practice you will see differences based on the data and sensors you use.  Just perform the balance calculations with different measurements, and you will see differences.  This is one good reason to look at all the data and what is predicted from the balance shot calculation.

Mixing velocity and displacement (or even acceleration)in a balance calculation takes some care and depends upon your means of calculation (balance program).  Velocity and displacement do not have similar magnitudes in general; this causes the balance program to prefer one or the other.  Either artificially change the magnitudes of one (multiply by a good constant, and remember it), or many programs have weighting available.
 
Of course you can use one and then the other in separate computations and compare the results.  If similar enough figure out what you might actually do, and calculate the effect of adding your shot.

Balancing does depend upon the person to some degree.  Good technique must be maintained by anyone in the game.

Thanks for your valuable suggestions.

I am  good in correction of Housing correction.

But in the case of Shaft vibrations, i have to do single plane correction or should do two planes at a time. 

I have seen some people doing single plane correction and checking the cross effect of that weight on the other plane  x and  y value and accordingly continuing the correction.

MHI using  software for reducing shaft vibrations.( recently they have done one comp. rotor balancing in our facility)

 

regards,

Ravishanker

Usually, I would check the balance calculation to see if a single plane works.

There is a potential issue with using too many balance planes (2 is not usually too many).  Many have experienced this with balance programs, when balance programs compute large (unexpectedly so) balance correction weights.  

It is simpler using fewer balance planes.  Measurement planes is another story.

Can you let us know on which machine you are working?? I will not talk much on balancing proedure as everyone else has already explained in a better way..if you see shaft vibration still high even after balancing then you may want to look for other issues which might not be reflecting well in casing vibration. Have you measured phase reading after balancing? If its a balancing issue whether you take casing vibration or shaft vibration it will not matter. And as per software so now a days almost all analyzer has option of vector balancing method also..but i generally requirement does not come for that. If yiu can share machine type, data and vibration plots and readings before and after balancing that will be helpful to all.

Sir,

I am using schenck high speed balancing machine. I have done more than 600 rotors balancing. (Turbine , comp.  and generator rotors) but i am not facing any problem in any rotor.

It is only for my learning purpose, in future if i face any  high shaft vibrations problem i wanted to attend them.

Ravishanker

 

You might look into a Dyrobes product which incorporates a optional component called RotorBal.  The RotorBal component is described at Rotorbal and the online manual is at RotorBal manual.

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