Shims more than 05 for 8 MW motor 1

[svkd]

Guys,
We have new machine motor 8 MW motor ,for motor to gearbox alignment the vendor has put shims around 8 to 9 shims ubder motor feet which is more than API recommended 5 shims.
We recommend vendor to arrange thick shims so as to reduce the no. Of shims upto 5. But vendor rejected our purposal and more than 5 shims are acceptable to vendor.

Just want to know can we accept this alignment with more than 5 shims?
OR what can we ask vendor regarding acceptable criteria for this motor with 8-9 shims under each feet?

 

[desertfox]

Hi

Was the vendor asked to supply shims to API?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[MintJulep]

Is it level and aligned?

 

[Tmoose]

I'd be a little interested in more detail beyond just the number of shims.
For instance -
- whether there are several very thin ( 0.005" or less) shims in each stack.
- Or four 0.125s and several fine tuning thin ones, etc.

- And if his reluctance to consolidate shims is due to the machine being a beeatch due to existing installation faults like a too thin bac\se, soft foot, pipe strain, being bolt bound, and etc.
Or, only has a bunch of 0.010 shims as his thickest ones.

 

[svkd]

Tmoose, The thickness of each shim is around 1mm , for alignment it requires to stack up to 9mm so he put 09 no.s of equal no of shims
My concern is no of shims more than 05.

Just want to know can we accept this alignment with more than 5 shims?
OR what can we ask vendor regarding acceptable criteria for this motor with 8-9 shims under each feet?

 

[Artisi]

Other than the inconvenience of handling so many shims under each foot, I see no valid reason to reject the equipment due to number of shims - as stated above, is it level and aligned.
Of course you can always insist on the standard being applied - but for what purpose?


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[svkd]

Guys/Artisi , the equipment is leveled and aligned , but my concern is more no of shims ? Is it going to create any problem like vibrations in future? What If in future motor replacement if we have to raise the motor for alignment? Usually the best practice is use atleast one thick shim(1/8 inch)at each feet so that vertical movement can be made if required.

 

[electricpete]

As I think you know, most millwrights are taught to limit number of shims.

There is some discussion of the reason on page 2 here where they recommend no more than 3

http://www.ludeca.com/brochures/Ludeca_Best-Practices-Machinery-Alignment-Shimming.pdf

They also give some discussion of ways to avoid too many shims (including a thick machined shim comes to mind if gap is large)

As desertfox alludes, depending on the situation sometimes the only leverage you have is what's invoked in the contract and associated standards.

Tmoose made some good points too


=====================================
(2B)+(2B)' ?

 

[whitetop]

It looks like you're in the range of 9mm shim allowance. Why not use two .125 solid shims and provide one .125 laminated shim under each motor foot. The laminated shim is peelable in 0.002 inch and available from AccuTrex Products, Inc. This gives you a range of .250 non-adjustable and .125 adjustable which is within the 9mm range using 3 shims under each foot.

 

[byrdj]

just for my curiousity, could you provide the plane diminsions and drawing/photo to see their simplicity or complixity.

My preferance would be to have two "thick shim", say ~3 to 4 mm with few thins sandwitched. and I would then not count the two thick

 

[Artisi]

svkd: If the holding down bolts are correctly torqued why will there be any vibration? -- and if you change motors in the future, you can address the shim/s requirements at that time, worrying about it at the moment is just spinning wheels for no reason.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[electricpete]

The reasons why people limit the number of shims? I have to admit I am not in a position to defend because I don't align machines myself. It seems that many shims make a spongy shim stack that is larger when loosened than tightened. It may make alignment process a little trickier. But if you pass a soft foot check beforehand and then pass an as-left alignment check afterward, I am not sure exactly what the remaining problem would be (by the way I wouldn't rely on absence of vibration to prove alignment is good since alignment can produce large static forces without time-varying/vibration-inducing forces). Maybe Tmoose or others can explain more specifically what is the concern and the basis for this thrumbrule limiting maximum number of shims.

But one thing I hope we can agree is that limiting the number of shims represents somewhat of a standard practice among millwrights. Two more references:

[ul]
[li]Piatrowski's Shaft Alignment Handbook
Some ‘‘rules of thumb’’ to follow for shimming machinery are:
1. Excluding the soft foot shims, you should not have more than five to six individual shims (or plates) under a foot to make an alignment correction shim ‘‘pack.’’[/li]
[li]GM Specification No. A1-2000
6.10.g - The overall shim pack shall not exceed a total of four (4) shims, including the SPACER BLOCK.[/li]
[/ul]

Like the op, it would certainly make me uneasy to notice that a standard practice was not being followed on a large machine (8 MW).

Possible remedies to seek are:
1 - attempt to fully understand the reason for the thumbrule in order to satisfy yourself why it's ok to deviate from it (and I don't think I'd be fully satisfied without agreement from someone that does alignment routinely)
- or -
2 - simply fix it. Perhaps you can loosen one foot at a time to replace the shims (with a fewer-number/same-thickness) and then retighten before going to next foot... without disturbing the alignment position (you'd probably want to recheck alignment afterwards to be sure, though).

=====================================
(2B)+(2B)' ?

 

[Strong]

Can the installer/aligner can prove or verify?
1) Correct size shims and material were installed
2) There is no Soft Foot by measurement at each foot and at coupling when loosening each base bolt at a time
3) Bolt strength and torque is correct
4) Alignment values meet required or precision tolerances (Sag corrected for dials, if used)
5) Vibrations are low and do not indicate misalignment or case distortion

A large number of shims (card deck) can be a tell-tale sign of a poor or shoddy alignment job, but if all else (see above) is good, then there should be no need to redo alignment solely to reduce shim count.

Walt

 

[MintJulep]

It is not trivial to align a machine of this size. It takes time and equipment - this is the likely cause of the vendor's reluctance.

Further, there is risk that they'll muck it up and leave it worse than it is now.

If it's level, aligned and stable let it be.

Restricting the number of shims to an arbitrary number is, well, arbitrary. If the performance requirements are met leave it be.

Next time you need to disturb the alignment for some other reason you can reduce the number of shims.

 

[Hoxton]

Just trying to remember from 40 years ago!

Was with the installation team installing a large motor generator set on a bedplate. I think this was 2500 mm by 10 000 mm (10ft by 25 ft). This was onto a concrete floor.

To cut a long story short, the process was to get the set level, with shim packs every 1 000 mm.

The highest point of the floor (least height of shim) was left with two by 0.5 mm shims

The number of shims in other shim packs I think was a max of 5

The reason given was that as shim stock (at that time) was punched or shear cut, that the shim would not be flat, and would act like a spring. Thicker shim could be saw or machine cut, but the problem then was the thinner ones.

So too much thin shim would result in a machine on a springy support, even if the whole bedplate was grouted onto the concrete floor after alignment.

So this was the old guys doing it by experience, no design input in those days!

The other thing I learnt was that they let me loose on no 2 set. The rule is that you add shim to the loosest shim pack. You end up with the plant creeping skywards... There is always In practice, one loose shim pack! It's the same reason why three legged stools never rock. You just cannot get all those shim packs exact. Experience rules... But the old guys never used too many shims. Perhaps with laser cut shims, you should reduce the max no of shims to three....

This post is dedicated to Alf and Rex who tought me how to align sets.

 

[desertfox]

Hi svkd

Actually I agree that there are to many shims and that thicker ones would be preferred however we cannot answer directly whether the installation is going to be okay or not because there are numerous other factors that are unknown to us here about the set up you have.

see web sites:-

http://reliabilityweb.com/articles/entry/best_practices_machinery_alignment_shimming/

http://ecmweb.com/motors/basic-motor-vibration-troubleshooting-tips

You could ask the installer to provide evidence of the alignment measurements they must have taken during set up i.e. bolt tightening preload and tightening sequence etc.

Now when I asked about the API spec, if they installer signed up to that then you can insist he changes the installation.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein