Taper shims for rotating equipment alignment

[svkd]

Guys,
We have observed taperness in a motor feet (due to poor machining) which is causing soft foot.Someone has suggested to make taper shims and put under motor feet to keep them in one leve.
Is it recommended to put tapered shim under motor feet to align it with pump.If taper shimming is permitted, how much should it be ?

 

[JJPellin]

I would not consider this to be a permanent solution. In situations when a unit shutdown would result, I have used step shimming to accommodate an angled foot. I do not understand you last question. The angled shim (or step shim arrangement) would be whatever angle exists between your machine foot and the base. The goal is to eliminate the soft foot condition. If the measured soft foot is less than 0.002 inch, then we would consider it to be acceptable.

As I noted, I would consider this to be a temporary repair and would make arrangements to remachine the base at the next opportunity.


Johnny Pellin

 

[svkd]

Johnny , What is the danger in using taper shim for long term? How it will effect the machine reliability?

 

[JJPellin]

Even if the specification for soft foot is achieved, there is likely to be some residual soft foot condition. This distorts the machine frame which can result in internal misalignment between the bearings. Motor frames are especially prone to this as they are generally not built as robust as a compressor or pump casing. Distortion of the motor frame can result in increased vibration at two times line frequency as a result of an uneven air gap between the rotor and stator.

Johnny Pellin

 

[svkd]

Thanks johnny for valuable inputs, One more query Can you give any idea on how much degree in taper shim can be allowed so that it cannot slipped off in running condition? My concern here is to ensure that the taper shim should not be act like a wedge.

 

[JJPellin]

If the bolt is properly tightened, I cannot imagine that the shim could walk out of the joint. I would not have any way to express a limit on how much angle is too much.

Johnny Pellin

 

[electricpete]

Our craftsmen are taught stepped shim method although it is not often used.

I don't see in what way tapered steel shim would be inferior to stepped shim (do you consider it inferior JJPellin?).

Either one seems like a reasonable permanent solution assuming we are not worried about movement. The only problem is that it takes more time any time the machine has to be realigned, especially if the technician is not aware of previous efforts and starts from scratch.

For reducing 2*LF vibration on 2-pole horizontal ball bearing motors with soft foot as a temporary measure, we have had reasonable success using precisionbrand "sof shims" (plastic shims). I would put these in temporary category because those plastic shims WILL have to be replaced every time you align the machine and by logic since they are "soft parts" may be more susceptible to age related degradation.

When we attempt permanent fix on those that we have installed soft shims, we have opted for machining the motor feet and (if necessary) the bases.


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(2B)+(2B)' ?

 

[dvd]

Here are a couple of other options -

http://www.chockingtimes.com/

http://www.chockfast.com/itwproducts.html