Journal/Sleeve Bearing Clearance

[RefineryRR]

How do equipment manufacturers determine the journal bearing clearances for their pumps, compressors, etc.?
Is there a rule-of-thumb for determining the optimal bearing clearances (metric)?
Do manufacturers use 'hyper-theoretical' means of determining these clearances? By this, I mean, do they use the fundamentals of hydrodynamics to determine the required shaft supporting force to ascertain what the correct clearances should be?

 

[burningDiesel]

Yes and yes.

A typical value is 0.001 of the shaft diameter.
But this can vary widely depending on:
- application: passenger cars will have less clearance, heavy power pumps will have larger clearance.
- oil used & oil temperature
- rotational speed & load
- ...

And yes, journal bearing manufacturers calculate this for you, usually using extended reynolds equations

 

[spciesla]

There are several rules of thumb, the one I'm most familiar with is 1.5 - 2.0 mils / inch of shaft diameter.

The July / August edition of Plant Engineering magazine (

http://www.plantengineering.com/magazine.html)

has an article about this topic starting on page 47.

http://bt.e-ditionsbyfry.com/publication/?i=328277#{"issue_id":328277,"page":0}

 

[tbuelna]

Do manufacturers use 'hyper-theoretical' means of determining these clearances? By this, I mean, do they use the fundamentals of hydrodynamics to determine the required shaft supporting force to ascertain what the correct clearances should be?

The design of radial journal bearings used on machinery like pumps and compressors can be quite complex. It can involve fluid mechanics, heat transfer, shaft dynamics, metallurgy, chemistry, etc. I doubt any legit OEM would be foolish enough to market a piece of machinery with journal bearings that were designed based on a "rule-of-thumb".

Here is an excellent public source technical reference that covers the basics of journal bearing design. Definitely worth a read.

 

[geesamand]

"Do manufacturers use 'hyper-theoretical' means of determining these clearances? By this, I mean, do they use the fundamentals of hydrodynamics to determine the required shaft supporting force to ascertain what the correct clearances should be?"

Depending on the speed of the plain bearing, lubricant type and delivery, and expected bearing life, hydrodynamic lubrication is not necessarily present. In cases of mixed-mode lubrication, plain bearings can operate very well and the designs will be based on rule-of-thumb and existing design references win the day. I was once involved in a dispute about a plain bearing design and it was very challenging to agree on best practices for design.

One major factor in clearance selection is angular misalignment - long thin shafts are not favorable for plain bearings and require more clearance.