clearance of 5 tilting pad journal bearing

[Hesam267]

hi everybody
we have 5 tilting pad journal bearing. in documents assemble clearance is 0.12_0.14 mm. this clearance is okay but when we install this bearing in our compressor clearance reduced extremely about 0.09 mm. so why and what can we do?

 

[JJPellin]

How did you measure the clearance of the bearing on the bench and in the machine?

Johnny Pellin

 

[Hesam267]

in machine with lifting shaft and in non assemble test we measure it with sample shaft (fix the shaft and move the bearing)

 

[JJPellin]

A lift check in an assembled machine can be difficult. Depending on the lifting method and the location of the dial indicator, the reading could be false high or false low. Did you verify the fit of the bearing within the housing? Excessive crush can reduce the installed clearance. Incorrect alignment between the upper and lower halves of the housing can alter the lift results. How are the two halves of the bearing connected? Are they bolted together? What type of pivots are used? Spherical, point contact, line contact? We need more information.

Johnny Pellin

 

[Tmoose]

http://www.orion-corp.com/Literature/Articles/Pivoted.aspx

 

[Hesam267]

thanx for your information
yes bearing halves bolted to each other. lifting the shaft is ok due its light weight. pivots are point contact and bearings are fit in housing completely. housing are align but im not sure about crush. is it real can reduce clearance?
how are other tilting pad behavior? are they same clearance in 2 method?
thanx agane

 

[Hesam267]

thank you Tmoose. we measure clearance in non assemble method like your link.

 

[JJPellin]

Yes. Excessive crush in the housing can reduce installed clearance. Did you place the dial indicator between the bearings or outside? What is the bearing span? If the rotor is very light, you can reduce the error by performing a parallel lift

Johnny Pellin

 

[Hesam267]

tkanx JJPellin .
we use double dial indicator two side of each bearing and calculate average.
so i think we must focus on Excessive crush as you said and can i say in journal tilting pad bearing assemble and non assemble clearance MUST be same in correct conditions?

 

[JJPellin]

The definitive test of the bearing clearance would be the bench test with a mandrel. The lift test as assembled in the machine is mainly to look for errors such as those we have already discussed. Since the lift test only checks one pad, it is not definitive of the bearing clearance. I would not expect the lift test to exactly match the bench test. Are you using a correction factor (0.8944) to adjust to the true clearance? Some equipment manufacturers based their clearance on the use of this correction factor. Some do not. You need to know if the manufacturer of your machine uses this correction factor or not when applying their clearance specification.

I assume that you have verified that the mandrel you used has the same diameter as the shaft journal.

Johnny Pellin

 

[Hesam267]

yes i consider 0.894 factor. and mandrel dia same as shaft.
so like you i think answer of question is in our previous chat. thank you again Johnny Pellin

 

[Khader001]

hi
is this centrifugal compressor with over hang impeller ?

I had a same experience if its over hang compressor the shat movement has to check in both directions down and up.
why don't measure the crush?

 

[Hesam267]

can you Explained how i can measure crush?
i heard two Definition about it.
1.it is clearance between top bearing and ID of housing
2.it is clearance between upper and lower housing while upper housing bolt tight with hand
i know actual that two are same but what is your suggestion or prefer?

 

[Tmoose]

""... .it is clearance between top bearing "

Upper bearing OD and the bearing housing. Probably negative clearance.

The second measurement could be made with hand tools and feeler gages with the machine mostly assembled.

 

[Hesam267]

actually our machine is old and non experts change its clearance before.
i dont know any idea about ID (housing bore) but bearing OD is 110mm and CM said it has looseness in system.
so dose it has any reference to determination clearance? what can i do?

 

[JJPellin]

I prefer to measure crush my comparing the bore of the housing to the outside diameter of the bearing. Typical crush might be 0 to 0.002 inch tight. But, this should be provided by the equipment manufacturer.

Johnny Pellin