vibration/alignment/balance

Hello gentlemen,

During shaft alignment of gearbox to pump/turbine, we referred to pump & gearbox manuals only to find unfamiliar presentation of shaft alignment. For example, the gearbox manual gives where its output shaft centerline would be relatively to the pump shaft, and vice versa. (In the attached sketch, the yellow circle represents the centerline of the gearbox output shaft and how it is shifted in x=0.4 mm & y=0.1 mm).

My question is, how to convert such presentation to the regular one, which is measured by dial gauge?

You can calculate the distance from the circle to the center and get the offset. However you cannot calculate angularity from this side of view.

Can you copy and post the actual plot that the manufacturer has provided?  

@Hans Bruckner posted:

You can calculate the distance from the circle to the center and get the offset. However you cannot calculate angularity from this side of view.

This was our original approach. But you can imagine the difficulty if the reference point was missed in the middle of the job. At the end we left it as (Which’s very close what we found during dismantling):

           0.1

0.0 ——-|-—— 0.1

           0.0

with the flexible coupling, we faced no issue and the vibration readings were acceptable.

@John Winterton posted:

Can you copy and post the actual plot that the manufacturer has provided?  

Currently I don’t have it. But it’s identical to the sketch attached.

What should be remembered is that for a gearbox with fluid film bearings there are four motions that need to be accounted for in the alignment process:

Vertical casing thermal growth
Vertical shaft motion within the bearing
Horizontal casing thermal growth
Horizontal shaft motion within the bearing

The rotor motions within the fluid bearing are due to gear generated forces and are dependent on the physical characteristics of the gearbox as well as the transmitted load.  (See attached)

Attachment(s)

forces.pdf   38 KB 1 version

@John Winterton posted:

What should be remembered is that for a gearbox with fluid film bearings there are four motions that need to be accounted for in the alignment process:

Vertical casing thermal growth
Vertical shaft motion within the bearing
Horizontal casing thermal growth
Horizontal shaft motion within the bearing

The rotor motions within the fluid bearing are due to gear generated forces and are dependent on the physical characteristics of the gearbox as well as the transmitted load.  (See attached)

 

I remember similar discretion in the manual.

Vertically: thermal upward growth + downward load =~ 0.1 mm

Horizontally: thermal side growth + side internal load (Both same direction) =~ 0.4 mm 

But We couldn't convert it to below format to our field technician to conduct the job

         ?

? ——|—— ?

         ?

@Muhannad Alzahrani posted:

I remember similar discretion in the manual.

Vertically: thermal upward growth + downward load =~ 0.1 mm

Horizontally: thermal side growth + side internal load (Both same direction) =~ 0.4 mm 

But We couldn't convert it to below format to our field technician to conduct the job

         ?

? ——|—— ?

         ?

If you do a search on this forum you might get a list like that found at https://www.maintenance.org/ad...agination.sort=SCORE  

Alignment is an often discussed topic and there have been a few spreadsheets posted.  

Here is some educational information:

Search: hot alignment procedure using dial indicators

https://www.bing.com/search?q=...M=ANNTA1&PC=U531

It is better to teach how to fish than to give a fish.

Walt

usually gearbox grows away from the dowel pin (fixed position), and upward

dowel pin |------------> thermal growth.

the +/- sign will depend on your dials but overal radial reading must be, after removing sag

(left-right)/2=0.40

(top-botom)/2=0.1

Mohammed, 

Your case is not unique. The method of stating operating positions (some prefer to refer to these as alignment targets) vary and sometimes for good reasons. 

For the sake of the argument, why you need to adjust the angularity? Perhaps there is none or it's not known to the manufacturer (specially the gearbox and motor manufacturers). If this chart is given by the gear manufacturer, this might be all they should provide.

Please keep in mind that shaft alignment is relative to the other machine and operating conditions. So, a gearbox would grow and move, to reasonable extent, to similar positions regardless of the driven equipment. However the alignment targets will vary a lot based on the driven equipment. The gearbox can drive a very cool or very hot service compressor so relative positions will change a lot. Compressor thermal expansion could play a big role in angularity (vertically).

Assuming that the chart is from the packager and it considers all factors, then the chart simply states not angularity. (You may want to verify that yourself).

I'm attaching an example of an old commissioning case (1979) that triggered my mind when I read your post. I hope it helps. (I dealt with this machine but I not there during the commissioning).

Regards- Ali M. Al-Shurafa

The second image refused to be uploaded.  I'm attaching it here again. I hope it accepts my attempt.

Regards- Ali M. Al-Shurafa

One approach with dial indicators that I have not seen much is to mount the indicators on the shaft to take some load of the bars.

Bill, can you please elaborate on this approach? "Bars" are the stems in the alignment fixtures?

Regards- Ali M. Al-Shurafa

When you mount the indicators on the shaft, you take the load off the bars for the alignment measurement.  You reduce bar sag by moving the indicator mass to the shaft.

If doing a face reading, this does not matter.   

The bars span from shaft to shaft for a reverse indication.  The lasers span the space without bars.

sag depends on your fixture, I've seen 5-7 mills on face readings, best is to measure the sag.

Excellent Pruftechnik Ltd. tutorial on alignment at A Practical Guide to Shaft Alignment

Bill,

Perhaps I understood your point. So, the indicator is vertically mounted on the shaft and it points up to the end of a horizontal bar coming from the other shaft. The bar may sag by its weight but no anymore by the wight of the indicator (the wight of the indicator is carried by the fixture on the shaft). Yes, though it is simple and looks practical, I've never seen it done. Thanks for sharing the method.

Regards- Ali M. Al-Shurafa

It is always a good idea to check bar sag.  At the big A plant in Saudi, I asked a technician what the bar sag was.  His replay was 0 without data.  I was very concerned because he was using tooling that comes with indicators.

We setup a shorter length  on a piece of pipe and measured.  It was at least 0.040 inches with the length around 1/2 of when he was aligning.  I figure he would have had 0.200 to 0.400 inches of sag; that would not have been a good alignment.  (Stiffness of the bar should be about a function of L cubed.)  Also, the using the tooling is not a good setup, either.  Throw a magnet in for good measure.  Proven method to break something.

@William Foiles posted:

It is always a good idea to check bar sag.  At the big A plant in Saudi, I asked a technician what the bar sag was.  His replay was 0 without data.  I was very concerned because he was using tooling that comes with indicators.

We setup a shorter length  on a piece of pipe and measured.  It was at least 0.040 inches with the length around 1/2 of when he was aligning.  I figure he would have had 0.200 to 0.400 inches of sag; that would not have been a good alignment.  (Stiffness of the bar should be about a function of L cubed.)  Also, the using the tooling is not a good setup, either.  Throw a magnet in for good measure.  Proven method to break something.

 

been there, 

one expert at a comisioning took his dial indicator and checked my laser alignment... it was a big fuz because he foun it 0.040 inches (1mm) off in the vertical, guess who learn to measure sag and who got an apology?

@William Foiles posted:

... I asked a technician what the bar sag was.  His replay was 0 without data.  I was very concerned because he was using tooling that comes with indicators.

We setup a shorter length  on a piece of pipe and measured.  It was at least 0.040 inches with the length around 1/2 of when he was aligning.  I figure he would have had 0.200 to 0.400 inches of sag; that would not have been a good alignment.. 

I'm not surprised when someone says no sag. I've heard that a lot. But I'm surprised that 0.20-0.40 inches are not visible by naked eyes!

Regards- Ali M. Al-Shurafa