Tilt Pad Bearing End Plate Clearance

[lugwrench]

I am trying to determine what the diametrical clearance for the endplates of a 5.25" ID tilt pad journal bearing should be. The assembled bearing clearance is .008" so the endplate clearance must obviously be something larger than this. I've found lots of literature on titl pad bearing design, but nothing on endplate clearances. Thanks in advance.

 

[electricpete]

what's an endplate?

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[lugwrench]

The endplates are bolted onto the side of the tilt pad bearing shell. They contain the oil and prevent axial movement of the pads. Check out page 5 of this link for a picture.

http://magnetic.waukbearing.com/__data/page/550/DHB10.pdf

 

[JJPellin]

I pulled the manual on a typical machine in our plant that uses tilt pad radial bearings. The maximum radial clearance in the bearing was 0.0032". The spec radial clearance for the end rings was 0.006". Note: Both of these are radial clearances, not diametral. Checking a few others, this seems to be typical. The end ring clearance seems to be about twice the bearing clearance. Of course, it is always best to get the exact specs from the equipment manufacturer for the particular bearing you are working with. All of the ones I looked at are load-between-pad. I don't think it would be different for load-on-pad, but I'm not certain. The last bearing I checked was for a 7" journal. The bearing clearance was nominal 4.5 mils radial. The end rings were 8 to 9 mils radial.

 

[diamondjim]

Please note that radial clearance and
diametral clearance are the same and
measured in the same way. It is the
total shift from a tight position
in one direction to the other direction.
A better terminology might have been
radial diametral clearance and axial
clearance for the side to side movement.

 

[JJPellin]

For the particular bearings that I was referring to, the radial and diametral clearances are not the same. These compressors are made by Elliott and they specify some clearances as radial (per side) and others as diametral (total clearance on the diameter) For the first bearing I mentioned, if you lift the shaft from bottom of the bearing to top of clearance you will register about 0.0064". The radial clearance is 0.0032". The diametral clearance is 0.0064". I don't know why some manufactures specify their clearances this way. It just leads to confusion. Interstage laby seals should have radial clearances specified because that is how you measure them. I am not aware of any method to measure clearance within a tilt pad radial bearing radially. You can check it on a mandrel or with a lift check. But, in both cases, you are measuring the diametral clearance.

 

[lugwrench]

Thanks guys. That's exactly what I was looking for.

 

[Mendit]

Fixed seal end plates are typical 0.002- 0.003 greater than the bearing clearance.
There are a floating seal types and these have 0.002-0.003 to the shaft and float independant of the housing.
When measuring lift on 5 pad bearings, beware, when the shaft is against 2 pads they tip together giving more clearance than actual, you must multiply the total lift by 0.899 to get the true clearance.

 

[JJPellin]

Mendit makes some good points. There are a number of different designs for end plates. All of the plates that I was checking are simple, fixed steel plates. These all had clearances that were about double the bearing clearance. I have seen other bearing designs where the end rings are babbit lined and can run closer clearances as a result. I have never come across a tilt pad radial bearing with floating end ring seals. But I would expect the clearance in this design to be even tighter yet. Lastly, you caught me in a mistake. The lift check that I mentioned would not yield the diametral bearing clerance on an odd-number pad bearing. It would be necessary to adjust the result for a between-pad lift.