Oil clearances in white metal sleeve bearings ? 2

[edison123]

Are there any rules/references on what should be the Oil clearances (side & top) for white metal sleeve bearings ?

Are the clearances related to speed / shaft dia ?

For example, what should be the clearances for a 160 mm dia shaft running at 3000 RPM ?

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[sms]

The general rule of thumb is that the bearing diametral clearance should be 0.0015 to 0.002 inches per inch of shaft diameter. so for a 4 inch diameter shaft the clearance would be 0.006 to 0.008 inches diametral.

I'll leave the conversion to metric to you. 1 inch=25.4 mm

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[edison123]

Thx sms.

Is there any web reference for this formula ?

Is it applicable for all speeds ?

* If a little knowledge is dangerous, then I am the safest person in the world *

 

[electricpete]

For motors, see EASA AR100 table 2-7. EASA recommends these values for use when OEM data is not available.

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[electricpete]

The 2001 version is available here:

http://www.easa.com/indus/ar100-2001.pdf

The table 2.7 mentioned is on page 12 of that document.

Interestingly, the table is removed from the 2006 version, and they just refer you to EASA Tech Manual Section 9.

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[electricpete]

The table in section 9 of the EASA Tech Manual is identical to table 2.7 of AR100 (2001).

One pattern you'll see if you look at the numbers is smaller shafts have higher ratio.
~2.5 mils/inch for 2" shaft
~ 2 mils/inch for 4" shaft
~ 1.5 mils/inch for 6" shaft
~ 1 mil per inch for 16" shaft

I have seen 1 mil per inch on 6" shaft associated with gearbox. I think in that case precise positioning of the shaft is important.

There are wide variations and a lot of design factors can drive it in different directions.

Speed could drive it either way. All other things being equal high speed machine is generally closer to instability which would drive toward smaller clearances, but high speed machine generates more heat which would drive towards higher clearances. Quite a number of other factors of course play into stability and temperature.

I have seen 6" shaft with one mil per inch specified by OEM for the sleeve bearings. It was on a gearbox. I think in that application precise control of shaft position is critical for proper gear operation.

Here on page 7,6th column you see tabulated fractional clearance c/d for a wide variety of applications. It seems many applications are close to c/d~0.001 which of course in one mil per inch. Maybe those are large applications?

http://www.uni-duisburg-essen.de/imperia/md/content/materialtechnik/lec_dt3_journal_bearings.pdf

For motors I don't think the variation is so wide and the EASA numbers are good. EASA is THE trade organization for US service shops and that AR100 standard is often invoked as part of a repair specification.

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[edison123]

Thx pete. As always, you are a saviour !

* If a little knowledge is dangerous, then I am the safest person in the world *