Motor Alignment

[Jaydubblazer]

Other than manufactuers recommendations what are some sources in determining what tolerances should be used for motor alighnment. I am in the process of gathering data for a plant and many of the pieces of equipment are one time pieces that don't have any information with them. Is there a way to look at existing equipment to determine this or some back-of-napkin process to at least get a maintenance program started. I realize that this is a very complex topic but if there is a guide to be used as a benchmark it would be very helpful.

Thanks

 

[thought2007]

Hi Jaydubblazer

I suggest to get motor shaft dimension details from Metrology,so its easier to carry further design process.


good luck

with regards
john

 

[waross]

Motor alignment;
Step one.> Check that the pulley is square on the shaft.
Use a level on the face of the pulley. Check the level, turn the shaft 90 degrees and re-check. Repeat for four positions.
Step two.> Use the same procedure to check the driven pulley.
Note; Level is best, if the installation is not perfectly level or the level is a bit off, the bubble must rest in the same place for all 8 checks. This will prove that the pulleys are installed straight and that both shafts are straight and parallel.
Step three.> Use a straight edge across both pulleys to check alignment. The straight edge should touch each edge of each pulley. I use a dollar bill to check for contact. Check each point of contact with a dollar bill. Insert the bill between the straight edge and the pulley at each point in turn. Pull the bill. There should be the same resistance to movement at each point of contact.
Sometimes a string may be used to double check the straight edge or in place of the straight edge. Experience and common sense helps a lot.
respectfully

 

[Skogsgurra]

And then, there are indicator clocks, laser aligners and all sorts of stuff. Google "motor alignment" for lots of information.

There is a difference between the "mils" people and the "microns" people. I think that best practice should be somewhere in-between.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[maytag]

Jay,
Tolerances will depend on a lot of variables i.e. RPM, load and the type coupling to be used to name only a few. If you are starting from scratch I would consider consulting with a firm that specializes in alignment, vibration analysis and balancing-
my 2 cents worth, Maytag

 

[rawelk]

Pumpzone has a good, short article on alignment

http://www.pump-zone.com/articles/39.pdf

Check out the motor manufacturer's recommondations. Westinghouse/Teco has a good section on alignment in their manual.

http://www.tecowestinghouse.com/Manuals/TWMC Instruction Manual_143 to 449 frame.pdf

The coupling manufacturer will also have limit specifications for angular and parallel alignment, and also a range for acceptable coupling-to-coupling distance.

Every so often I've run across installations where the motor and driven couplings were in good parallel and angular alignment, but nearly butted up against each other. This is a BAD idea, because, as the shafts grow due to temperature increase during operation that clearance is almost certain to be lost.

My generic rule of thumb for 50 HP and higher power is 0.001" for up to 1800 RPM, and 0.0005" for higher speeds. You can get away with more misalignment (but not much more) when rotational speeds, and power transferred is lower.

All misalignment is eventually expressed as heat, and greater stress in the mechanical system (shafts, bearings, couplings, etc.).

Time pressure to get a machine running again can't be ignored, but can't be the sole determining factor, either.

I recall an instance where a 50 HP process pump motor had at least twice in a 48 hour period snapped off several mounting bolts, and chewed through several elastomer coupling inserts. Turned out alignment was in the 0.065" range (I think the coupling was rated for 15 or 20 mil max misalignment).

In this case the entire plant went down shortly after this pump stopped operating (it's backup unit was out for repair), and we didn't have time for a spot-on alignment, but was able to get it within 10 mil using straightedge and feelers for an extra 15 minutes worth of work, and it stopped failing catastrophically.

 

[Jaydubblazer]

Thanks for the comments. I have since went through the motors and determined which are critical motors. Everything over 250 HP will be laser aligned. Everything between 20-249 HP will be at 1-3 mil dependent on RPM (requiring a dial indicator for these alignments). I am sitting down next week with a design engineer to determine these.

I still have the smaller motors (1/2-19 HP) that I could use some help on. As rawelk had noted many of the flexible couple manufactures have rather large tolerances for alignment, I have seen as much as 30 mil. I want to align these as close as possible but not pay to have all motors in the plant aligned to 1 mil or less. I also don't want to pay for a new coupling every other month becuase we are following the manufactures recommendations.

 

[superdumpy]

Hello Jay,

I'm in the process of writing up a standard operating procedure for the allignment of pulleys and shafts. did you manage to get much literature on this issue. any help would be great.

kind regards,
Thomas Byrne

 

[Jaydubblazer]

The links that rawelk gave helped and talking to some millrights and get there opinions. If you can find some of the literature for the equipment that you already own, you find that there are many simularites that can be used for a SOP.

Wes

 

[superdumpy]

Thanks Wes,

I'll have a look around and see what I can dig. Do you have your own SOP for this? What are the chances getting a look at that?
Company policy permitting of course....
Regards,
Thomas
Thomas

 

[Tmoose]

Don't forget to make an effort to compensate for thermal effects.

Do the specs for this new equipment include permissable vibration?

 

[superdumpy]

Hi Tmoose,

These are actually old units and I have little in the way of specs. The fan and motor are kept in an air stream chamber of roughly 14 degress celcius.

Cheers
Thomas