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Alex

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Reply with quote  #1 
I have a question about thermal growth at coupling alignment. You can calculate it by yourself or use some of the available calculators.....
In each case you need to enter both side temperatures. I saw one calculator that uses foot and base temperatures.
Now I wonder... what about bearing or shaft temperatures? They can be significantly different from side to side and much more differ. I have a case where foot temperature difference is ten times lower then shaft temperature difference.

What is your experience, recommendation. Thank you
OLi

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Reply with quote  #2 
It is the longest piece of iron or material and the largest temp diff that give the most expansion in my book.


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electricpete

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Reply with quote  #3 
I don't have a lot of experience in those calculations myself.   But I still have an opinion:

In theory, everything below the shaft centerline that expands would count, including the lower half of the shaft and bearing. 

Let's say pump shaft centerline is supported by several chunks of height H1, H2, H3 etc.
When it heats from ambient to operating each section experiences a deltaT.
Each section has a known thermal expansion coefficient alpha. 
The total growth below of the pump shaft centerline is H1*alpha1*DeltaT1 + H2*alpha2*DeltaT2 + H3*alpha3*DeltaT3...
Compare that to total growth of everythign below motor centerline which is usually much smaller. 

You could if you want include the shaft radius (not shaft diameter since half is above centerline) as H1. 
And you could include the bearing thickness-per-side as H2 (accounting for only the lower half of the bearing). 
Maybe these are neglected in many cases because the heights tend to be small compared to what's below them. But if the temperature differences are much larger then I vote yes, include them.

In the end we know it may not ending up being a very good estimate due to many unknowns, and measurements of actual thermal growth on the relevant machinery when available will trump any calculations. 


jvoitl

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Reply with quote  #4 
With the IR camera and software I use I can get the average temperature of a line from the bottom of the foot to the shaft centerline of a machine and the change from ambient to running temperatures.  Using this and the coefficient of expansion for the material I've tried to see how close I could get to the factory spec.  In one case of a large blower, the factory said .014 and I came up with .013.
Shurafa2

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Reply with quote  #5 
A very important concept here is relativity.

Is the dimensional change expansion or contraction with respect to the original dimension?

Is the expansion with respect to the point of interest in the horizontal, vertical or axial direction?

What matters more is the relative expansion (not the expansion of a single point). For example, DE to NDE of a pump or DE of pump to DE of motor.

What is the reference temperature reference? 60, 70, 80, 90 or 100 F ? By the way it is very hot here nowadays.

Regards- Ali M. Al-Shurafa
Alex

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Reply with quote  #6 
I found this calculator named Thermal_Growth_Master_311 on the other forum:
https://www.maintenance.org/topic/need-thermal-growth-formula?reply=399590942963533153#399590942963533153 

As I understand the instructions, temperatures should be measured at each foot (contact between the machine and the base). Is this suitable enough?


OLi

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Reply with quote  #7 
It is not the foot that is doing the thermal expansion? It is the normally iron btw. the floor and the shaft I thought and it is the avg. temp of that, that counts I think. I agree, that is vertically but as far as I remember, that are the problems I have had IRL.
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dnk

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Reply with quote  #8 
Vibralign made attachments that mounted on bearing housings. After alignment they were left on and run machine until it reached running temperature. From that you could tell how much growth and what direction it moved. I was surprised to see that machines do not grow evenly in all directions, especially old machines that mounts have been modified.
OLi

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Reply with quote  #9 
Yes used the same from EasyLaser/Damalini earlier this year but we left them on during the test sequence and triggered measuremnts to get some trending. That machine in that respect was moving as OEM expected, eg it kept the same across the coupling as we measured across it as it was the movement across the coupling that was interesting if that was good for the type of coupling that was used could be argued, they will get a new coupling for next operating season after the summer.....
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Shurafa2

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Reply with quote  #10 
Oli,

Do the lasers calculate the axial growth affecting the DBSEs?

Regards- Ali M. Al-Shurafa
OLi

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Reply with quote  #11 

We used this accessory  https://easylaser.com/en-us/products/accessories/bracketing/dm-bracket

glued to the bearings at each side of the coupling and we just used the basic measurement software giving dial type readings H/V and you could
set the reading to 0 / 0 when cold to direct read the change to hot state in full operation. So any further calc of derived things you need to do yourself as far as I know.
It was a quick thing that came up with short notice so we just hired the complete kit, did the testrun and extracted the data from the device.

We also had a eddy probe against the coupling hub axially and it moved to the end position right when the machine tripped on vibration so the couplng locked up but that is another story. It is a brand new turbine, never so far reached full load w/o trip.


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106Bones

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Reply with quote  #12 
There is no program that can split a moving hair like this topic is. The key word is not thermal growth its alignment. Measure it, growth or shrinkage, at the feet, the centerline or on piping stresses its the alignment resultant in what often is a thermally variable application that should be the focus. Few applications operate in such a steady state without thermal changing that the numbers will be un changing and forever finite. Knowing the applicable parameters and aligning within those parameters is the start, predicting changes and establishing best operating adjustments requires brain work and investigation not short cut thermal growth apps.     
RustyCas

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Reply with quote  #13 
I think it’s very important to be able to do your own thermal growth calculations. You really only need to know the thermal growth coefficient, the change in temperature for the part in question (or the “average” change), and the dimensions of the part. As you start to work through the calculations you will come to understand what matters a little, and what matters a lot.

Doing your own calculations you will discover there are different classes of machines, some where thermal growth can almost be ignored (run-of-the-mill pumps and fans), some where it’s a moderate concern, and some where it’s critical.

Learning how to measure temperatures of operating machines to develop a thermal profile (to get the “average” temperature change) is an important skill, as is being able to look at a machine an determine “how” it’s going to grow (simple example: the difference in growth at each end of a TEFC motor).

As Bones points out, there are no shortcuts - it’s a skill, developed like any other skill, through acquired knowledge and practice.

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Big Al

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Reply with quote  #14 
It's been a few years since I last did a laser alignment, but there were a few critical machines that we would return to after running them up to temperature and carry out a hot alignment. Have all the thermal growth calculators made this practice redundant now?
Walt Strong

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Reply with quote  #15 
"we would return to after running them up to temperature and carry out a hot alignment."

Big Al,

How long did it typically take you to Lock Out and Tag out, remove coupling guard, set up laser, and make measurements? What type and size of machines did you do this procedure? Was the vibration lower after the Hot Alignment compared to before?

Walt
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